Concrete Resources

Aggregate Sizes Chart

Reference chart for all construction aggregate sizes — fine aggregate grading zones (IS 383), coarse aggregate nominal sizes (10mm, 20mm, 40mm), road aggregate specifications (GSB, WMM, MOT Type 1), and drainage gravel — with international equivalents, sieve size tables, and application selection guide.

Last updated: June 22, 2026

Aggregate size is specified differently depending on the application, the country, and the standard being used. A structural drawing may call for '20mm aggregate' while a road specification calls for 'WMM' and a drainage contractor asks for '20mm single-size clean stone' — three different materials requiring three different products despite the same number appearing in each description.

This guide provides a complete reference chart for all aggregate sizes used in construction — fine aggregate grading zones, coarse aggregate nominal sizes, road aggregate specifications, and drainage gravel — with IS 383:2016 sieve requirements, international equivalents, bulk density reference values, and an application selection guide.

How Aggregate Size is Defined

Aggregate size is defined by sieve analysis — passing the material through a series of sieves with decreasing aperture sizes and measuring what percentage of the total sample passes each sieve. The result is a cumulative passing curve that must fall within the grading envelope specified by the relevant standard.

Nominal Size

The commercial designation — the sieve size that most of the aggregate passes. '20mm aggregate' passes the 20mm sieve. A small percentage may be retained. Used for ordering and specification.

Maximum Size

The smallest sieve through which 100% of the aggregate passes. Always larger than nominal size. Used for structural checks per IS 456:2000 Clause 5.3.1 — must not exceed ¼ of the minimum member dimension.

Grading Zone

For fine aggregate — the IS 383 zone (I to IV) defined by the cumulative percentage passing key sieves. Zone determines application suitability. Not applicable to coarse aggregate, which uses nominal size.

The 4.75mm sieve is the boundary between fine and coarse aggregate in IS 383:2016. Material passing 4.75mm is fine aggregate (sand); material retained on 4.75mm is coarse aggregate. This boundary sieve is the same across IS, ASTM, and BS EN standards.

IS Sieve Series with International Equivalents

IS sieves use metric aperture sizes. The table below lists every sieve in the IS 383 series with the closest ASTM and BS EN equivalents — useful when reading specifications that mix Indian and international standards or when sourcing aggregate from international suppliers.

IS Sieve Size	Aperture (mm)	ASTM Equivalent	BS EN Equivalent	Key Use
80mm	80.0	—	—	GSB Grade I, large sub-base, gabion
63mm	63.0	—	—	GSB, WBM, large rock fill
53mm	53.0	—	—	GSB Grade II upper limit
40mm	40.0	1½ inch	37.5mm	40mm coarse aggregate, PCC, WMM upper
20mm	20.0	¾ inch	19.0mm	20mm coarse aggregate — standard concrete
12.5mm	12.5	½ inch	12.5mm	Bituminous concrete wearing course
10mm	10.0	⅜ inch	9.5mm	10mm coarse aggregate, precast, drainage
6.3mm	6.3	¼ inch	6.35mm	Single-size pea gravel, chip seal
4.75mm	4.75	No. 4	4.75mm	Fine/coarse boundary — IS 383 dividing sieve
2.36mm	2.36	No. 8	2.36mm	Fine aggregate grading — Zone I/II boundary
1.18mm	1.18	No. 16	1.18mm	Fine aggregate grading — mortar sand check
600 µm	0.600	No. 30	0.600mm	Key sieve for grading zone classification
300 µm	0.300	No. 50	0.300mm	Fine aggregate — plaster sand check
150 µm	0.150	No. 100	0.150mm	Fine aggregate lower limit; micro-fines check
75 µm	0.075	No. 200	0.075mm	Silt/clay boundary — IS 383 silt test reference

ASTM inch-fraction sieves (¾ inch = 19.0mm) do not exactly match IS metric sieves (20mm). For compliance testing, always use the sieve series specified in the governing standard — do not substitute ASTM sieves for IS sieves or vice versa without confirming equivalence with the testing authority.

Fine Aggregate Grading Zones — IS 383:2016

IS 383:2016 classifies fine aggregate into four grading zones. Each zone specifies the permissible range of cumulative percentage passing at each sieve size. Zone II is the standard for concrete; Zone IV is the standard for plastering. The 600µm sieve is the key sieve for zone classification.

Cumulative % Passing — IS 383:2016 Grading Limits

IS Sieve Size	Zone I (Coarsest)	Zone II	Zone III	Zone IV (Finest)
4.75mm	90–100	90–100	90–100	95–100
2.36mm	60–95	75–100	85–100	95–100
1.18mm	30–70	55–90	75–100	90–100
600 µm	15–34	35–59	60–79	80–100
300 µm	5–20	8–30	12–40	15–50
150 µm	0–10	0–10	0–10	0–15

Values are cumulative % passing. All material must pass the 4.75mm sieve (100%) and the maximum % passing 150µm is 10% for Zones I–III and 15% for Zone IV. Source: IS 383:2016 Table 4.

Zone Characteristics and Applications

Zone	Particle Character	600µm Passing	Best Application	Notes
Zone I	Coarsest	0–10% passing 600µm	Sub-base fines, limited concrete use	Rarely produced; generally too coarse for concrete or mortar
Zone II	Medium-coarse	35–59% passing 600µm	Concrete (most common), floor screed	Standard concrete sand — river sand and M sand Zone II
Zone III	Medium-fine	60–79% passing 600µm	Concrete, masonry mortar, external plaster	Better workability than Zone II; slightly higher water demand
Zone IV	Finest	80–100% passing 600µm	Internal plaster, pointing, masonry mortar	P-sand (plastering M sand); river sand Zone IV; smooth finish

IS 456:2000 Clause 5.3.2 states that Zone IV fine aggregate should not be used in reinforced concrete unless tests have been made to ascertain its suitability. The fine particles in Zone IV increase water demand, which must be controlled by reducing the water-cement ratio or using a water-reducing admixture.

Estimating sand quantity for concrete, mortar, or plastering?

Use our Sand Weight Calculator →

Coarse Aggregate Sizes — IS 383:2016

Coarse aggregate (material retained on the 4.75mm sieve) is classified by nominal size. IS 383:2016 specifies grading limits for each nominal size in terms of the percentage passing the nominal sieve and the sieve one size below. The table below summarises the standard sizes, their sieve range, typical bulk density, and primary construction applications.

Size / Grade	Sieve Range	Max Size (IS 456 check)	Bulk Density (kg/m³)	Primary Applications
40mm nominal	Passes 40mm, retained 20mm	75mm max	1,500–1,600	Mass concrete, PCC, large footings, retaining walls, blinding
20mm nominal	Passes 20mm, retained 10mm	40mm max	1,550–1,650	Standard RCC — slabs, beams, columns, footings (most common)
10mm nominal	Passes 10mm, retained 4.75mm	20mm max	1,580–1,650	Thin sections, pump concrete, congested reinforcement, precast
Graded 40mm (40–10mm)	Mixed 40mm and 20mm particles	40mm max	1,600–1,700	Combined gradation per IS 383 Table 2 — used in some mix designs
Graded 20mm (20–10mm)	Mixed 20mm and 10mm particles	20mm max	1,600–1,680	Alternative to single-size 20mm; better packing, lower void content
Angular crushed (all sizes)	From jaw/cone/VSI crusher	Per size above	1,550–1,700	Higher bond strength than rounded; standard for structural RCC
Rounded (river gravel)	Naturally rounded particles	Per size above	1,450–1,520	Better workability; lower bond than crushed; used in non-structural fill

IS 456:2000 Clause 5.3.1 limits maximum aggregate size to the smallest of: (a) ¼ of the minimum member dimension, (b) clear spacing between bars minus 5mm, and (c) clear cover minus 5mm. For a 150mm column with 25mm cover and 20mm bars at 40mm spacing: limit is min(37.5mm, 35mm, 20mm) = 20mm. Always verify 20mm aggregate against these three checks before specifying.

Need to calculate coarse aggregate quantity for your project?

Use our Aggregate Weight Calculator →

Need aggregate quantities for a specific concrete grade?

Use our Mix Design Calculator →

Road and Sub-Base Aggregate Specifications

Road construction uses a layered system where each layer has a specific aggregate grading requirement. Unlike concrete aggregate (which is specified by nominal size), road aggregate is specified by grading envelope — the full particle size distribution must fall within defined limits. Maximum size alone is not sufficient for road aggregate specification.

Layer / Type	Grading Description	Max Size	Bulk Density (kg/m³)	Application
GSB — Grade I	75mm down to dust, well-graded	75mm	1,650–1,750	Granular Sub-Base first layer; IRC SP:49
GSB — Grade II	53mm down to dust	53mm	1,650–1,750	GSB upper layer; finer gradation than Grade I
WMM (Wet Mix Macadam)	40mm down to dust, graded	40mm	1,750–1,900	Road base course; MORTH Clause 406
WBM (Water Bound Macadam)	90mm / 63mm / 45mm single-size + screenings	90mm	1,600–1,750	Older base course; largely replaced by WMM
Bituminous Macadam (BM)	40mm nominal, graded	40mm	1,700–1,800	Binder course in flexible pavements; MORTH Clause 504
DBM (Dense Bituminous Macadam)	19mm or 26.5mm nominal	26.5mm	1,800–1,950	Base/binder course; MORTH Clause 507
BC (Bituminous Concrete)	13.2mm nominal	13.2mm	1,900–2,100	Wearing course; MORTH Clause 509
SDBC / Semi-Dense BC	13.2mm nominal	13.2mm	1,850–2,050	Wearing course for lower traffic volume roads
MOT Type 1 (Crusher Run)	0–40mm, well-graded	40mm	1,850–1,950	UK standard sub-base; increasingly used in India for driveways
MOT Type 2	0–40mm, may include recycled material	40mm	1,750–1,900	UK sub-base; lower specification than Type 1; non-trafficked areas

Do not substitute single-size aggregate for graded road aggregate. GSB and WMM require a well-graded mix from maximum size down to fines — the fines fill the voids between larger particles and provide stability under compaction. Single-size stone does not compact into a stable base and will shift under traffic load.

Drainage and Landscaping Aggregate Sizes

Drainage aggregate is the opposite of road sub-base: it must be single-size (or nearly so) to maintain open voids between particles that allow water to flow freely. The key quality requirement is low fines content — less than 5% passing the 75µm sieve — because fines migrate into voids and reduce drainage performance over time.

Type / Size	Grading	Max Particle	Bulk Density (kg/m³)	Application
Pea gravel (6–10mm)	Single-size	10mm	1,450–1,500	Pipe surround, filter blanket, small soakaways
10mm single-size	Single-size crushed or rounded	10mm	1,500–1,550	Perforated pipe surround, filter layer, drainage blanket
20mm single-size	Single-size crushed	20mm	1,500–1,580	French drain, soakaway crates, drainage trench fill
40mm single-size	Single-size crushed	40mm	1,450–1,550	Large soakaways, infiltration trenches, heavy-duty drainage
Gabion stone (50–150mm)	Large angular rock	150mm	1,400–1,600	Gabion baskets, retaining walls, riverbank protection, erosion control
Rip-rap (100–300mm)	Large angular rock / boulders	300mm	1,350–1,550	Riverbank protection, slope stabilisation, coastal defence
Filter media (2–5mm)	Clean grit/gravel	5mm	1,500–1,600	Rapid sand filter layers, bioretention systems, SUDS filter media

Never compact single-size drainage aggregate. Compaction forces angular particles to rotate and interlock, closing the inter-particle voids and converting a free-draining layer into a nearly impermeable one. Drainage aggregate should be placed and levelled without mechanical compaction — its own weight provides sufficient settlement for structural stability in drainage applications.

Calculating gravel or drainage aggregate for a trench, soakaway, or path?

Use our Gravel Weight Calculator →

Bulk Density Reference — All Aggregate Types

Bulk density is the mass of aggregate per unit volume including inter-particle voids, measured in kg/m³. It is the conversion factor between volume (measured on site) and weight (quoted by the supplier). Loose bulk density applies to material poured freely; rodded bulk density applies to compacted material. Use loose bulk density for ordering calculations.

Aggregate Type	IS 383 Category	Loose Bulk Density (kg/m³)	Rodded Bulk Density (kg/m³)
River Sand (Zone II)	Fine aggregate	1,550–1,650	1,700–1,780
M Sand / Manufactured Sand (Zone II)	Fine aggregate	1,700–1,800	1,850–1,950
M Sand Zone IV (P-sand)	Fine aggregate	1,650–1,750	1,800–1,880
10mm Crushed Granite	Coarse aggregate	1,580–1,650	1,700–1,780
20mm Crushed Granite	Coarse aggregate	1,550–1,650	1,680–1,760
40mm Crushed Granite	Coarse aggregate	1,500–1,600	1,630–1,700
Crushed Limestone (20mm)	Coarse aggregate	1,450–1,550	1,580–1,640
River Gravel / Pea Gravel (10–20mm)	Coarse aggregate	1,450–1,520	1,580–1,640
GSB (Granular Sub-Base)	Road aggregate	1,650–1,750	1,850–1,950
WMM (Wet Mix Macadam)	Road aggregate	1,750–1,900	1,950–2,100
MOT Type 1 / Crusher Run	Sub-base	1,850–1,950	2,050–2,150
Recycled Concrete Aggregate (RCA)	Coarse aggregate	1,100–1,400	1,300–1,550
Gabion Stone / Large Rock	Structural fill	1,350–1,600	—

All values are dry condition. Wet aggregate weighs 8–20% more per volume. Values vary by quarry source, particle shape, and grading. For critical estimates, use the supplier's tested bulk density value.

Want to measure your aggregate's bulk density from a site field test?

Use our Aggregate Density Calculator →

Aggregate Size Selection Guide — by Application

The table below gives the correct aggregate size or specification for every common construction application, with the governing IS or international reference and key notes on selection criteria.

Application	Correct Aggregate	Governing Standard	Key Selection Note
RCC slab (100–200mm thick)	20mm nominal crushed granite	IS 383:2016 Table 2	Standard for all residential slabs
RCC beam (width ≥ 200mm)	20mm nominal crushed granite	IS 383:2016 + IS 456	20mm well within ¼ minimum dimension rule
RCC column (150–300mm)	20mm nominal or 10mm if congested	IS 456:2000 Cl. 5.3.1	Check clear cover and bar spacing before selecting 20mm
RCC footing (≥ 300mm thick)	20mm or 40mm nominal	IS 456:2000	40mm reduces cement content; suitable for large isolated footings
PCC (plain concrete blinding)	40mm nominal	IS 456:2000	Coarser aggregate acceptable; reduces cost of non-structural concrete
Pump-placed concrete (100mm pipe)	20mm maximum	ACI 304.2R, IS 456	20mm ≤ ⅓ × 100mm pipe = 33mm limit
Precast elements, thin sections	10mm nominal	IS 383 + IS 1343	Thin precast panels and prestressed members need finer aggregate
Mass concrete (dams, large walls)	40mm or 80mm	IS 456:2000 Cl. 5.3	Larger aggregate reduces heat of hydration; structural engineer to specify
Road sub-base (residential/commercial)	GSB Grade II or MOT Type 1	IRC SP:49 / SOR	Well-graded 0–40mm; must be compacted
Road base course	WMM (0–40mm)	MORTH Cl. 406	Mechanically laid and roller compacted
Bituminous wearing course	13.2mm (BC)	MORTH Cl. 509	Wearing course — size governs surface texture and skid resistance
Driveway sub-base (block paving)	MOT Type 1 (0–40mm), 150mm compacted	UK Spec / IRC	Well-graded; must compact to stable base under vehicle load
French drain / soakaway	20mm single-size clean stone	BS EN 12620 / IS 383	Single-size; no fines; maintains drainage voids — do not compact
Perforated pipe surround	10mm single-size or pea gravel	BS EN 1610 / IRC 34	Fine enough to prevent pipe perforations being blocked by stone
Gabion basket fill	50–150mm angular rock	BS EN 13383 / IS 1597	Large enough to not pass through gabion mesh aperture
Decorative garden gravel	10mm or 20mm rounded/washed	No standard	Aesthetic choice; rounded is more comfortable underfoot
Concrete block bedding layer	Sharp sand (0–5mm) Zone II	BS 7533 / IS 2116	Fine sharp sand, not building sand — provides stable bedding plane

International Size Equivalents

Projects with international consultants, imported specifications, or materials sourced from outside India need to reconcile IS 383 size designations with ASTM, BS EN, and AS equivalents. The table below gives the closest equivalents — note that sieve sizes do not match exactly and compliance must be verified against the actual grading envelope, not just the size designation.

IS 383 Designation	ASTM C33 Equivalent	BS EN Equivalent	AS Equivalent
IS 383: 10mm nominal	ASTM C33: No. 8 (9.5mm–2.36mm)	BS EN: 4/10mm	AS 2758.1: 10mm
IS 383: 20mm nominal	ASTM C33: No. 57 (25mm–4.75mm) approx	BS EN: 10/20mm	AS 2758.1: 20mm
IS 383: 40mm nominal	ASTM C33: No. 4 (37.5mm–4.75mm)	BS EN: 20/40mm	AS 2758.1: 40mm
IS 383: Fine (Zone II)	ASTM C33: Fine aggregate	BS EN 12620: 0/4mm	AS 2758.1: Fine aggregate
IS 383: Fine (Zone IV / Plaster)	ASTM C144: Masonry sand	BS EN 13139: 0/2mm	AS 3972 fine sand
GSB (IRC SP:49)	ASTM D2940 (Graded Aggregate)	BS 7533 Sub-base	AS 1289 (subgrade)
MOT Type 1 (Crusher Run)	ASTM D2940 Cl. A	Spec for Highway Works Cl. 803	VicRoads Schedule 204

ASTM size numbers (No. 57, No. 8) refer to grading envelopes, not particle sizes — the number is a historical designation, not a millimetre size. ASTM No. 57 (25mm–4.75mm) is the closest equivalent to IS 383 20mm nominal but the grading limits are not identical. For compliance purposes, test against the actual standard's grading envelope.

Relevant Standards

Indian Standards

Standard	Coverage
IS 383:2016	Specification for Coarse and Fine Aggregates — primary Indian standard defining grading zones, nominal sizes, sieve requirements, and quality limits for all construction aggregate
IS 2386 (Part I) – 1963	Methods of Test for Aggregates: Particle Size and Shape — sieve analysis procedure for determining grading zone and nominal size compliance
IS 456:2000	Plain and Reinforced Concrete — Clause 5.3.1 governs maximum aggregate size limits relative to structural member dimensions, reinforcement spacing, and cover
IS 1343:2012	Prestressed Concrete — specifies finer aggregate limits (10mm max) for prestressed members due to thin sections and duct congestion
IRC SP:49	Guidelines for Granular Sub-Base — defines GSB grading envelopes (Grade I and Grade II) and compaction requirements for road sub-base layers
MORTH Specifications	Ministry of Road Transport and Highways — Specifications for Road and Bridge Works; defines WMM, BM, DBM, and BC aggregate grading envelopes for each road layer
IS 1597 (Part 1):1992	Construction of Stone Masonry — includes gabion and stone fill specifications for retaining structures

International References

Standard	Coverage
ASTM C33 / C33M	Standard Specification for Concrete Aggregates (USA) — uses size numbers (No. 57, No. 8, etc.) and inch-fraction sieves; the primary US reference for concrete aggregate grading
ASTM D2940	Graded Aggregate Material for Bases or Subbases for Highways or Airports (USA) — covers graded sub-base aggregate equivalent to GSB/MOT Type 1
BS EN 12620:2002+A1:2008	Aggregates for Concrete (UK/EU) — defines nominal size using d/D notation (e.g. 10/20mm); European standard for concrete aggregate classification
Specification for Highway Works, Cl. 803	UK Highways England — defines MOT Type 1 (unbound mixture) grading requirements for sub-base construction
AS 2758.1	Aggregates and Rock for Engineering Purposes: Concrete Aggregates (Australia) — covers 10mm, 20mm, 40mm nominal sizes for concrete with Australian sieve designations
AS 1289	Methods of Testing Soils for Engineering Purposes (Australia) — includes sub-base aggregate grading and compaction standards

Final Verdict

Aggregate size selection is not a single decision — it depends on the structural element, the application type, the placement method, and the governing standard. For most Indian residential RCC work, 20mm crushed granite (IS 383:2016 compliant) covers the majority of requirements. The exceptions that must be caught before ordering are thin members or congested reinforcement (10mm), large PCC elements (40mm), plastering (Zone III–IV fine aggregate), drainage (single-size clean stone, no compaction), and road sub-base (graded GSB or WMM, not single-size).

Default to 20mm crushed granite for all standard RCC elements — slabs, beams, columns, and footings where section dimensions allow.
Check IS 456:2000 Clause 5.3.1 for three limits before confirming 20mm: ¼ minimum member dimension, clear bar spacing minus 5mm, and clear cover minus 5mm.
Specify fine aggregate by grading zone, not just 'sand' — Zone II for concrete, Zone III–IV for plastering. Zone II M sand is unsuitable for plastering.
Use graded aggregate (GSB, WMM) for road and driveway sub-base — single-size stone will not compact into a stable base.
Use single-size clean stone (no fines) for drainage — graded aggregate blocks drainage voids over time.
Never compact single-size drainage aggregate — compaction destroys drainage performance.
For pump-placed concrete, confirm aggregate maximum size does not exceed ⅓ of the pump line diameter.

Related calculators

Use these calculators when you need to turn this reference information into project quantities:

Aggregate Weight Calculator
Calculate aggregate quantity by weight from project dimensions — supports all aggregate types, wastage, compaction, and moisture.
Aggregate Density Calculator
Measure and verify bulk density, void content, and specific gravity of aggregate from IS 2386 field tests.
Aggregate Unit Converter
Convert between cubic metres, cubic yards, brass, kg, tonnes, quintals, US tons, bags, and truck loads.
Concrete Mix Design Calculator
Estimate coarse and fine aggregate quantities within a concrete mix for M20 and other grades.
Concrete Calculator
Estimate total concrete volume and material quantities for slabs, beams, columns, and footings.
Gravel Weight Calculator
Calculate gravel for driveways, drainage, paths, and sub-base applications in multiple shape modes.

Related resources

Aggregate Quantity Guide
How to calculate aggregate quantity for any construction project. Covers estimation methods, bulk density, wastage, compaction, IS 383 and IS 2386 standards, unit conversions, and worked examples for concrete, sub-base, backfill, and drainage.
20mm vs 40mm Aggregate Guide
Understand the difference between 20mm and 40mm coarse aggregate for concrete. Covers IS 456 size rules, workability, strength, cost, typical applications, and when to use each size.
M Sand vs River Sand
Complete comparison of M sand (manufactured sand) and river sand for construction. Covers IS 383:2016 grading zones, bulk density, silt content, water absorption, concrete workability, plastering performance, availability, cost, and environmental impact.
Concrete Mix Ratios Explained
Understand concrete mix ratios such as 1:2:4, 1:1.5:3, 1:3:6, 1:4:8, and 1:5:10, including grades, uses, water-cement ratio, curing, and cost.
M20 Concrete Guide
Understand M20 concrete, including 20 MPa strength, 1:1.5:3 nominal mix ratio, common RCC applications, standards, curing, compaction, mistakes, and site checklist.
Water-Cement Ratio Guide
Understand water-cement ratio in concrete, including formula, recommended W/C values, strength and durability effects, water per cement bag, exposure limits, and common site mistakes.

FAQ

20mm nominal maximum size coarse aggregate is the standard for M20 concrete in most Indian residential and commercial construction. IS 456:2000 Clause 5.3.1 states that the maximum aggregate size should not exceed one-quarter of the minimum dimension of the structural member. For a 125mm slab, 20mm aggregate is well within this limit. For a 100mm column, 20mm is also acceptable. 10mm aggregate is used when a finer mix is needed — for thin sections, congested reinforcement, or pump-placed concrete. 40mm aggregate is used for mass concrete elements such as large footings, retaining walls, and PCC layers where the section is deep enough to accommodate larger particles.

Nominal size is the sieve size through which the majority of the aggregate is required to pass — it is the commercial designation. Maximum size is the smallest sieve size through which 100% of the aggregate passes. For '20mm nominal' aggregate per IS 383:2016, the aggregate is retained on a 10mm sieve and passes a 20mm sieve — but some particles may be retained on the 20mm sieve (up to a small percentage). The maximum size is therefore defined by the sieve at which essentially all material passes. In practice, '20mm aggregate' means the material's characteristic particle size is around 20mm, and the maximum particle present is close to 25mm. Using nominal size for specification and maximum size for structural checking (IS 456:2000 Clause 5.3.1) reflects this distinction.

Use 10mm aggregate when: the minimum dimension of any structural member is less than 75mm; reinforcement spacing is less than 40mm clear; concrete is being pump-placed through a small-diameter pump line (75mm or 100mm bore); or the mix design targets high workability with low water content (aggregate smaller than 10mm has more surface area, which improves bonding but increases water demand). Use 20mm aggregate as the default for all standard slabs, beams, columns, and footings where section dimensions allow. 20mm aggregate produces a more economical mix (less cement required for the same strength) and is more widely available. For most residential RCC work, 20mm is the correct choice unless the structural drawings specify otherwise.

Indian road construction uses a layered sub-base and base course system with specific aggregate gradations for each layer. Granular Sub-Base (GSB) uses a graded mix of 75mm down to fines, specified in IRC SP:49. Wet Mix Macadam (WMM) uses 0–40mm graded aggregate per MORTH specifications. Bituminous Macadam (BM) uses 40mm down stone. Dense Bituminous Macadam (DBM) uses 19mm or 26.5mm nominal size stone. Bituminous Concrete (BC, wearing course) uses 13.2mm nominal maximum aggregate. Each layer has a specific grading envelope — the aggregate must be tested against that grading requirement, not just specified by maximum size. IRC 111 and MORTH Specifications for Road and Bridge Works are the primary references.

Drainage aggregate is specifically chosen to remain open-graded — it must not compact into a dense mass that blocks water flow. Single-size aggregate (also called single-grade or clean stone) is used: 10mm single-size for filter layers and perforated pipe surround; 20mm single-size for French drains and soakaways; 40mm single-size for large soakaways and infiltration trenches. Pea gravel (6mm–10mm rounded stone) is used for small perforated pipe surround and drainage blankets. The critical requirement is that drainage aggregate must have less than 5% fines passing a 75-micron sieve — any more and the fine material migrates into and blocks the drainage voids. Do not use crusher run or GSB (which contain fines) for drainage applications.

ASTM C33 uses size numbers rather than millimetre designations. The closest equivalents are: IS 383 20mm nominal ≈ ASTM C33 No. 57 (25mm–4.75mm); IS 383 10mm nominal ≈ ASTM C33 No. 8 (9.5mm–2.36mm); IS 383 40mm nominal ≈ ASTM C33 No. 4 (37.5mm–4.75mm). The sieve sizes in ASTM use inch-fraction designations (3/4 inch = 19mm, 1½ inch = 37.5mm) which do not exactly match IS 383 metric sieves. For projects that span IS and ASTM specifications, always verify the actual sieve analysis against the applicable standard's grading envelope — do not rely on approximate equivalences for compliance.

For pump-placed concrete, the aggregate maximum size must not exceed one-third of the internal diameter of the pump line. For a 100mm diameter pump line (the most common size on residential sites), the maximum aggregate size is 33mm — making 20mm aggregate the safe standard choice. For a 75mm diameter pump line (used in restricted-access situations), the limit is 25mm — again making 20mm nominal aggregate the correct specification. Using 40mm aggregate in a 100mm pump line risks blockage at bends and reducers. If 40mm aggregate is specified in the structural mix design but pump placement is needed, either switch to 20mm aggregate with an adjusted mix design or confirm the pump diameter is at least 120mm.

MOT Type 1 (Crusher Run, 0–40mm graded aggregate) is the standard sub-base material for driveways and paved areas in the UK and is increasingly used in India for the same application. It is a graded mix from 40mm down to dust that compacts into a dense, stable layer. The 'Type 1' grading specification ensures the material locks together when compacted rather than shifting under load. Do not use single-size aggregate (such as 20mm clean stone) as a sub-base — it will not compact and will shift under vehicle loading. After the Type 1 sub-base, a bedding layer of sharp sand (Zone II, 0–5mm) or grit sand is placed before paving blocks or slabs.