Steel Resources

TMT Bar Weight Chart

TMT bar unit weight chart for all diameters 6mm to 40mm — kg/m, kg per 12m rod, weight formula (D²/162), bundle quantities, and bar bending schedule (BBS) calculation walkthrough with worked examples for slabs, beams, and columns.

Last updated: June 22, 2026

Steel is ordered and paid for by weight — tonnes or kilograms. But structural drawings specify bars by diameter and spacing. Converting between the two requires the unit weight of each bar diameter, applied to every bar in a bar bending schedule. A 5% error in unit weight across a 20-tonne steel order is 1 tonne of steel — either over-ordered and wasted or under-ordered and short.

This chart gives the unit weight (kg/m), weight per 12m rod, weight formula derivation, mass tolerance, and typical bar count per tonne for every standard TMT bar diameter from 6mm to 40mm — with IS 1786:2008 grade reference, bar bending schedule weight calculation method, and worked examples for slabs, beams, and columns.

The D²/162 Formula — Derivation and Use

The standard formula for TMT bar unit weight is W = D² ÷ 162, where W is in kg/m and D is the nominal diameter in mm. This comes from:

Derivation:

Cross-sectional area = π × D² ÷ 4 (mm²)

Steel density = 7,850 kg/m³ = 7,850 × 10⁻⁶ kg/mm³

Weight per mm length = (π × D² ÷ 4) × 7,850 × 10⁻⁶

Weight per metre = above × 1,000

= (π × 7,850 ÷ 4,000) × D²

= 0.006165 × D² ≈ D² ÷ 162.2 ≈ D² ÷ 162

Bar Diameter	Formula	Calculation	Unit Weight
6mm	6² ÷ 162	36 ÷ 162	0.222 kg/m
8mm	8² ÷ 162	64 ÷ 162	0.395 kg/m
10mm	10² ÷ 162	100 ÷ 162	0.617 kg/m
12mm	12² ÷ 162	144 ÷ 162	0.889 kg/m
16mm	16² ÷ 162	256 ÷ 162	1.580 kg/m
20mm	20² ÷ 162	400 ÷ 162	2.469 kg/m
25mm	25² ÷ 162	625 ÷ 162	3.858 kg/m
32mm	32² ÷ 162	1024 ÷ 162	6.321 kg/m

D²/162 gives the theoretical nominal weight. IS 1786:2008 permits actual bar weight to vary by ±7% (for 6mm–10mm) and ±5% (for 12mm and above) from nominal. Always use nominal weight for BBS calculations — adjust the total order quantity upward by 5–7% to account for tolerance and wastage, not for individual bar weights.

TMT Bar Weight Chart — All Standard Diameters

IS 1786:2008 standard diameters for deformed TMT bars: 6, 8, 10, 12, 16, 20, 25, 28, 32, 36, and 40mm. The 12mm and 16mm bars are by far the most used in Indian residential slabs; 20mm and 25mm dominate beam and column reinforcement.

Diameter	Area (mm²)	Unit Weight (kg/m)	Weight per 12m Rod (kg)	Bars per Tonne (12m rods)	Typical Application
6mm	28.3	0.222	2.67	375	Stirrups in light beams, distribution bars in light slabs, spacers
8mm	50.3	0.395	4.74	211	Stirrups and ties — standard for residential beams and columns
10mm	78.5	0.617	7.40	135	Distribution bars, secondary slab steel, light column ties
12mm	113.1	0.888	10.66	94	Slab main bars, secondary beams, hanger bars, column ties in light columns
16mm	201.1	1.580	18.96	53	Standard slab main bars, primary beams in residential construction
20mm	314.2	2.469	29.63	34	Primary beam main bars, column longitudinal bars — most common structural bar
25mm	490.9	3.858	46.30	22	Heavy beams, column bars in multi-storey buildings, transfer beams
28mm	615.8	4.834	58.01	17	Commercial structure beams and columns with high load demand
32mm	804.2	6.313	75.75	13	Long-span or heavily loaded commercial beams, large columns
36mm	1017.9	7.990	95.88	10	Large columns and transfer elements in high-rise buildings
40mm	1256.6	9.864	118.37	8	Very heavily loaded columns, industrial structures, bridges

Unit weights calculated using D²/162 formula. Bars per tonne calculated as 1,000 ÷ (weight per 12m rod). Standard bar length = 12m per IS 1786:2008.

IS 1786:2008 Steel Grades Reference

IS 1786:2008 classifies TMT bars into grades based on yield strength, UTS, elongation, and ductility. The grade does not affect the unit weight — a 20mm Fe 415 bar and a 20mm Fe 500 bar weigh the same. Grade affects strength, development length, and seismic suitability.

Grade	Min Yield Strength (N/mm²)	Min UTS (N/mm²)	Min Elongation	Min UTS/YS Ratio	Use
Fe 250	250	≥ 410	≥ 23%	Not specified	Plain mild steel; rarely used in modern RCC
Fe 415	415	≥ 485	≥ 14.5%	≥ 1.10	Older standard TMT grade; still on some drawings
Fe 415D	415	≥ 500	≥ 18%	≥ 1.12	Higher ductility; preferred in seismic zones
Fe 500	500	≥ 545	≥ 12%	≥ 1.08	Standard TMT grade for all current residential construction
Fe 500D	500	≥ 565	≥ 16%	≥ 1.10	Higher ductility; recommended by IS 13920 for seismic zones
Fe 550	550	≥ 585	≥ 10%	≥ 1.06	Used in commercial, high-rise, and infrastructure projects
Fe 550D	550	≥ 600	≥ 14.5%	≥ 1.08	Higher ductility variant of Fe 550
Fe 600	600	≥ 660	≥ 10%	≥ 1.06	High-strength grade; bridges and industrial structures

Fe 500 is the standard grade for all current residential and commercial construction in India. Fe 500D is strongly preferred for seismic zones — the higher elongation ensures the bar can undergo significant plastic deformation before fracturing, giving the structure time to absorb earthquake energy without sudden collapse. Specify Fe 500D by name on project drawings — do not assume suppliers will upgrade from Fe 500 without explicit specification.

IS 1786 Mass Tolerance — Acceptable Weight Range

IS 1786:2008 Table 3 specifies allowable tolerance on nominal mass per unit length. Understanding this range is important when verifying delivered bars against the order weight, and when assessing whether a supplier's bars are within specification.

Diameter	Mass Tolerance (IS 1786)	Acceptable Unit Weight Range (kg/m)	Acceptable Weight per 12m Rod (kg)
6mm	±7%	0.206–0.238	2.48–2.86
8mm	±7%	0.367–0.423	4.40–5.07
10mm	±7%	0.574–0.660	6.88–7.92
12mm	±5%	0.844–0.933	10.12–11.20
16mm	±5%	1.501–1.659	18.01–19.91
20mm	±5%	2.346–2.592	28.15–31.10
25mm	±5%	3.665–4.051	43.98–48.61
32mm	±5%	5.997–6.629	71.96–79.55

Bars at the lower tolerance limit (–5% to –7%) deliver less steel per tonne than nominal — a tonne of under-weight 20mm bars contains more bars but each bar is structurally lighter. For structural acceptance, verify unit weight against IS 1786 limits, not just the diameter. Request mill test certificates from the manufacturer for all structural steel deliveries.

Bar Bending Schedule — Weight Calculation Method

A bar bending schedule (BBS) lists every bar in the structure with its diameter, shape code, cut length, count, and weight. The weight calculation follows a consistent method for all bar shapes.

BBS Weight Calculation:

Weight of one bar = Cut length (m) × Unit weight (kg/m)

Weight of bar mark = Weight per bar × Number of bars

Total steel = Sum of all bar mark weights + wastage factor

Example — Bar mark B1: 20mm, straight, 4800mm, 8 nos.:

Unit weight = 20² ÷ 162 = 2.469 kg/m

Cut length = 4.800m

Weight per bar = 4.800 × 2.469 = 11.85 kg

Total for B1 = 8 × 11.85 = 94.8 kg

Cut Length by Shape Code

Shape / Shape Code	Cut Length Basis	Weight Calculation
Straight bar (shape A)	Total bar length = L	L × unit weight
90° bend (L-bar, shape B)	L1 + L2 + 2× bend allowance	(L1 + L2 + deduction) × unit weight
Stirrup — rectangular (shape R)	(2×a + 2×b) + 2 hooks allowance	Perimeter + 2×(hook extension) × unit weight
Stirrup — square (shape S)	4×a + 2 hooks allowance	Perimeter + hook allowance × unit weight
U-bar (shape U)	L1 + L2 + L3 (bottom)	(L1+L2+L3) × unit weight
Cranked bar (bent-up bar)	Horizontal + inclined length + hook	Full cut length × unit weight
Column main bar with hook	Column height + lap + 2×hook	Total cut length × unit weight
Slab bar with standard hook	Span + 2× support embedment	Total cut length × unit weight

Cut length includes hook extensions — the physical length of bar that is ordered. The structural length (what appears on the drawing dimension) is shorter than the cut length by the hook allowance at each end. SP 34 Table 2 provides standard hook extension allowances by bar diameter and hook type. Always use cut length (not structural length) for weight calculations.

Stirrup Weight Reference — Common Beam and Column Sizes

Stirrup weight is often underestimated in preliminary estimates. For standard residential beams, stirrups typically account for 15–25% of the total beam steel weight. The table below gives the weight per stirrup for common beam and column sizes using 8mm and 10mm bar.

Stirrup Configuration	Perimeter (mm)	Hook Allowance (mm)	Cut Length (mm)	Unit Weight (kg/m)	Weight/Stirrup (kg)	Stirrups per kg
150×200mm, R8 stirrup	700	100	800	0.395	0.316	3.16
200×300mm, R8 stirrup	1000	100	1100	0.395	0.435	2.30
230×380mm, R8 stirrup	1220	100	1320	0.395	0.521	1.92
230×430mm, R8 stirrup	1320	100	1420	0.395	0.561	1.78
230×530mm, R8 stirrup	1520	100	1620	0.395	0.640	1.56
300×500mm, R10 stirrup	1600	100	1700	0.617	1.049	0.95
Column tie 230×230mm, R8	920	100	1020	0.395	0.403	2.48
Column tie 300×300mm, R8	1200	100	1300	0.395	0.514	1.95

Hook allowance of 100mm per stirrup is used (2 × 50mm hook extension for 90° hooks on 8mm bars). For IS 13920 seismic 135° hooks on 8mm bars, hook extension = 10φ = 80mm per hook; add 160mm total to perimeter. Verify with actual hook specification on the structural drawing.

Worked Examples

Three complete examples applying the weight chart to real steel quantity takeoffs for slabs, beams, and columns.

Example 1 — Steel Weight for a Residential RCC Slab (BBS Method)

India — Standard residential

An 8m × 6m RCC slab, 125mm thick, two-way. Bottom steel: 12mm bars at 150mm c/c both directions. Top steel at edges: 10mm bars at 200mm c/c. Slab perimeter = edge strips 1.2m wide. Calculate total steel weight.

Step	Formula / Value	Result
Bottom bars — 12mm @ 150 c/c, 8m direction	Count = 6000 ÷ 150 + 1 = 41 bars; Length = 8000 + 2×150 (hook) = 8300mm	41 × 8.3m × 0.888 kg/m = 302.1 kg
Bottom bars — 12mm @ 150 c/c, 6m direction	Count = 8000 ÷ 150 + 1 = 55 bars; Length = 6000 + 300 = 6300mm	55 × 6.3m × 0.888 kg/m = 307.6 kg
Top bars — 10mm @ 200 c/c, edge strips (8m edges)	Count = 6000 ÷ 200 + 1 = 31 bars; Length = 1200 + 1200 = 2400mm each	31 × 2.4m × 0.617 kg/m × 2 edges = 91.9 kg
Top bars — 10mm @ 200 c/c, edge strips (6m edges)	Count = 8000 ÷ 200 + 1 = 41 bars; Length = 2400mm each	41 × 2.4m × 0.617 kg/m × 2 edges = 121.7 kg
Total steel (net)	302.1 + 307.6 + 91.9 + 121.7	823.3 kg
Add wastage (5% — standard bars)	823.3 × 1.05	864.5 kg → order 0.87 tonnes

This is a simplified BBS illustration. Actual BBS must include every bar mark with shape code, exact cut length (including hooks and laps), and must be prepared by or reviewed by the structural engineer. The hook extension assumed here is 150mm per end for 12mm bars (12 × 12 = 144 ≈ 150mm).

Example 2 — Stirrup Steel Weight for a Series of Beams

India — Residential first floor

6 beams of 230mm × 450mm, each 5m span. Stirrups: R8 @ 150mm c/c throughout (simplified). Calculate stirrup weight for all 6 beams.

Step	Formula / Value	Result
Number of stirrups per beam	5000 ÷ 150 + 1 = 34 stirrups	34 stirrups per beam
Total stirrups (6 beams)	34 × 6	204 stirrups
Cut length per stirrup (230×430mm internal, R8)	2×(230+430) + 2×(8×10) hooks = 1320 + 160	~1380mm (use 1400mm with tolerance)
Total length of 8mm bar	204 × 1.40m	285.6m
Unit weight of 8mm bar	0.395 kg/m	—
Total weight (net)	285.6 × 0.395	112.8 kg
Add wastage (5%)	112.8 × 1.05	118.5 kg → order 0.12 tonnes of 8mm bar

Stirrup hook length: IS 13920 requires 135° hooks with 10φ extension for seismic detailing. For 8mm bars, each hook extension = 10 × 8 = 80mm. For non-seismic 90° hooks, extension = 12φ = 96mm. The hook allowance per stirrup end is 80–96mm — add 160–192mm to the bare perimeter for hook stock.

Example 3 — Column Bar Schedule for Ground to First Floor

India — 2-storey residential

Column 230mm × 300mm with 6T16 longitudinal bars (Fe 500). Ground floor to first floor height = 3.3m. Lap at starter = 1.0m below ground slab. Floor-to-floor height = 3.3m. Calculate column bar weight.

Step	Formula / Value	Result
Column bar length (ground to first floor)	3300 (floor height) + 1000 (lap below) + 500 (above first floor slab)	4800mm per bar
Number of bars	6 bars (T16)	—
Total length of 16mm bar	6 × 4.8m	28.8m
Unit weight — 16mm bar	1.580 kg/m	—
Net weight	28.8 × 1.580	45.5 kg
Add wastage (3% — CTL bars)	45.5 × 1.03	46.9 kg → order with other column bars

Column starter bar length includes the lap below the slab (typically 40φ–50φ for Fe 500) and an extension above the next floor slab for the next level's lap. The 500mm extension above the slab is used when bars continue to the next floor; if this is the top floor, bars are bent into the roof slab or terminated with a hook.

Quick Weight Reference — Common Bar Lengths

The table below gives the weight (kg) for the most common bar lengths and diameters encountered in residential construction — useful for quick cross-checking without calculation.

Bar Length	8mm	10mm	12mm	16mm	20mm	25mm
1.0m	0.40	0.62	0.89	1.58	2.47	3.86
1.2m	0.47	0.74	1.07	1.90	2.96	4.63
2.0m	0.79	1.23	1.78	3.16	4.94	7.72
3.0m	1.19	1.85	2.66	4.74	7.41	11.57
4.0m	1.58	2.47	3.55	6.32	9.88	15.43
4.5m	1.78	2.78	3.99	7.11	11.11	17.36
5.0m	1.98	3.09	4.44	7.90	12.35	19.29
6.0m	2.37	3.70	5.33	9.48	14.81	23.15
8.0m	3.16	4.94	7.10	12.64	19.75	30.86
10.0m	3.95	6.17	8.88	15.80	24.69	38.58
12.0m	4.74	7.40	10.66	18.96	29.63	46.30

All values in kg. Calculated using D²/162 × length. Values rounded to 2 decimal places.

Common Mistakes

Using D²/162 Without Knowing It Gives Nominal Weight

The D²/162 formula gives the theoretical weight based on nominal diameter and steel density. Actual bar weight can differ by up to ±5–7% within IS 1786 tolerances. For a large steel order of 50 tonnes, a 5% under-weight delivery means the building contains 47.5 tonnes of actual steel instead of 50 — a 2.5-tonne deficit spread through the structure. For critical structural work, verify the actual unit weight on delivery by weighing a sample bar and comparing to D²/162 × bar length. Under-weight bars are a common issue with non-BIS-certified suppliers.

Not Accounting for Hook Extensions in Cut Length

The cut length of a bar (what is ordered and paid for) includes the hook extensions — the bar must be cut longer than the structural dimension to form the hooks. A 180° hook requires additional bar length of approximately 4φ (bend radius) + 4φ (straight) = 8φ beyond the bend point. Many BBS sheets list the 'centre-line' length without adding the hook stock, which leads to bars being ordered too short to form the correct hook. SP 34 gives the standard hook extension allowances for each shape code.

Ordering Steel by Count Without Checking Diameter Identity

A request for '50 bars of 16mm' can be fulfilled with bars that are nominally 16mm but marginally underweight (within the ±5% tolerance). A simpler error is receiving 16mm bars in a mix of grades (Fe 415 and Fe 500 in the same bundle) — which can happen with non-certified suppliers mixing heats. Always verify bar diameter with a vernier calliper on delivery (not just visual inspection — ribs look similar across grades), and check the manufacturer's test certificate for yield strength and elongation to confirm the grade.

Calculating Stirrup Quantity Without Including the First and Last

The count formula 'span ÷ spacing + 1' is frequently misapplied. For a 5000mm beam with stirrups at 150mm c/c, the correct count is (5000 ÷ 150) + 1 = 33 + 1 = 34 stirrups — the '+1' adds the closing stirrup at the far end. Omitting the '+1' gives 33 stirrups and leaves the last 150mm zone without a stirrup. On a 6-beam floor with this error, that is 6 missing stirrups. More significantly, the first and last stirrups at the support face should be placed at 50mm from the face — this first spacing is not the same as the general spacing, and must be tracked separately in the BBS count.

Confusing kg/m with kg per Rod for Ordering

Unit weight (kg/m) is used to calculate total weight from a length. Weight per rod (kg per 12m bar) is used to plan delivery and storage. Mixing these up — for example, ordering in 'kg/m' quantity when the supplier expects 'total kg' — leads to gross over- or under-ordering. The safest ordering method is: total length in metres × unit weight (kg/m) = total weight in kg, then divide by 1,000 for tonnes. Never call a supplier with only a bar count or a metres figure without also specifying the total weight as a cross-check.

Relevant Standards

Standard	Coverage
IS 1786:2008	High Strength Deformed Steel Bars and Wires for Concrete Reinforcement — specifies grades (Fe 415, Fe 500, Fe 500D, Fe 550, Fe 600), nominal diameters, mass tolerances, yield strength, UTS, elongation, and bend test requirements for all TMT bars
IS 456:2000 Table 65	Provides IS code reference for development lengths by bar diameter and steel grade, derived from the same unit weight values as this guide
IS 2502:1963	Code of Practice for Bending and Fixing of Bars for Concrete Reinforcement — defines standard shape codes, bend radii, hook extensions, and cut length calculations for BBS preparation
IS 13920:2016	Ductile Detailing — recommends Fe 500D or Fe 415D over standard Fe 500 or Fe 415 for seismic zones; specifies hook extensions for 135° hooks used in seismic stirrups
SP 34:1987 (BIS)	Handbook on Concrete Reinforcement and Detailing — provides standard bar bending schedule format, shape code reference, and hook/bend allowance tables used in BBS preparation
IS 1387:1993	General Requirements for the Supply of Metallurgical Materials — governs delivery, testing, and acceptance conditions for TMT bars including mass per unit length verification

Final Verdict

TMT bar weight calculation is the foundation of every steel quantity takeoff. The D²/162 formula gives the nominal unit weight for any bar diameter in seconds; the BBS method applies that weight to every bar mark in the structure to produce an accurate, verifiable order quantity. The most important practical points for residential construction are the four numbers used every day: 0.395 (8mm stirrups), 0.888 (12mm slab bars), 1.580 (16mm slab/beam bars), and 2.469 (20mm beam/column bars) — all in kg/m.

Use D²/162 for any bar diameter — memorise the four key values: 8mm = 0.395, 12mm = 0.888, 16mm = 1.580, 20mm = 2.469 kg/m.
Always calculate cut length (including hook extensions) for weight — not the structural drawing dimension.
Apply 3–5% wastage for CTL (cut-to-length) supply; 5–7% for site-cut from 12m bars.
Specify Fe 500D (not Fe 500) for all primary structural members in seismic zones — same weight, same cost, significantly higher ductility.
Verify bar weight on delivery for large orders — weigh a sample bar against D²/162 × measured length.
Use the stirrups per kg values in the reference table to cross-check on-site stirrup consumption against order quantities.

Ready to calculate beam steel weight with a full BBS output?

Use our Beam Steel Calculator →

Calculating slab reinforcement quantities?

Use our Slab Steel Calculator →

Related calculators

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

Beam Steel Calculator
Calculate main bars, stirrups, and total steel weight for RCC beams per IS 456:2000 and SP 34.
Slab Steel Calculator
Calculate main bars, distribution bars, and total steel for RCC slabs — one-way and two-way.
Column Steel Calculator
Estimate longitudinal bars, lateral ties, and total steel weight for RCC columns.
Footing Steel Calculator
Calculate reinforcement for isolated and combined footings with bar bending schedule output.
Concrete Calculator
Estimate total concrete volume and material quantities for slabs, beams, columns, and footings.

Related resources

Beam Reinforcement Guide
Complete guide to RCC beam reinforcement per IS 456:2000 and SP 34. Covers tension and compression bars, stirrup spacing, minimum and maximum steel percentages, clear cover, detailing rules, bar bending schedule, and common reinforcement mistakes.
Development Length Guide
Complete development length (Ld) reference for RCC construction per IS 456:2000 Table 65. Covers all bar diameters, steel grades (Fe 415, Fe 500, Fe 550), and concrete grades (M15 to M40) — with worked examples for beams, slabs, columns, and footings, plus anchorage, lap splice, and hook equivalence rules.
RCC Slab Thickness Guide
Understand common RCC slab thickness values for residential rooms, roof slabs, larger spans, commercial floors, and industrial applications, including span guidance, standards, concrete volume, cover, reinforcement, and curing.
Concrete Cover Guide
Understand concrete cover thickness for RCC slabs, beams, columns, footings, water tanks, retaining walls, cover blocks, corrosion protection, fire resistance, and common site mistakes.
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.
Construction Material Wastage Guide
Complete reference for construction material wastage percentages. Covers concrete, bricks, cement, sand, steel reinforcement, tiles, paint, plaster, and timber — with IS code references, worked examples, and site reduction tips.

FAQ

The unit weight of a TMT bar per metre length is calculated using the formula: W = D² ÷ 162, where W is the weight in kg/m and D is the nominal diameter in mm. This formula is derived from the density of steel (7,850 kg/m³) and the cross-sectional area of a circular bar (π × D² ÷ 4). For a 16mm bar: W = 16² ÷ 162 = 256 ÷ 162 = 1.580 kg/m. For a 20mm bar: W = 20² ÷ 162 = 400 ÷ 162 = 2.469 kg/m. This formula gives the nominal weight; IS 1786:2008 allows a tolerance on actual weight of ±7% for bar diameters up to 10mm and ±5% for 12mm and above.

TMT bars in India are supplied in standard lengths of 12 metres per IS 1786:2008. Some manufacturers also supply 10m and 11.5m lengths, but 12m is the most common and is the standard assumption in bar bending schedules. Bars can also be ordered as cut-to-length (CTL) where the supplier cuts bars to specific lengths from the BBS — this reduces on-site cutting wastage from 5–7% (site-cut from 12m bars) to 2–3% (CTL). For very short bars (stirrups, ties, spacers), suppliers sometimes supply pre-bent bars or coiled rod in 6mm and 8mm diameters.

TMT bars are supplied in bundles of varying quantities depending on diameter. Typical bundle configurations per IS 1786 practice: 6mm — 50 to 100 bars per bundle; 8mm — 40 to 60 bars; 10mm — 25 to 40 bars; 12mm — 20 to 30 bars; 16mm — 10 to 15 bars; 20mm — 7 to 10 bars; 25mm — 5 to 7 bars; 28mm — 4 to 6 bars; 32mm — 3 to 5 bars. Bundles are typically 2–3 tonnes each to allow handling by crane or forklift. Exact bundle quantities vary by manufacturer — confirm with the supplier before planning unloading and storage.

Fe 500D is a higher ductility variant of Fe 500 TMT bars, classified under IS 1786:2008 as a separate grade. Both have the same minimum yield strength (500 N/mm²) but Fe 500D has tighter requirements on the UTS/YS ratio (minimum 1.10 vs 1.08 for Fe 500) and on total elongation at fracture (minimum 16% vs 12% for Fe 500). The 'D' stands for ductile. IS 13920:2016 (seismic design) recommends Fe 500D or Fe 415D over standard Fe 500 or Fe 415 for primary structural members in seismic zones III, IV, and V, because the higher ductility allows more plastic deformation before fracture — giving a structure more warning before collapse. For seismic zone III and above, specify Fe 500D, not Fe 500.

Total steel weight from a bar bending schedule is calculated by: (1) listing every bar mark with its diameter, shape, number of pieces, and cut length; (2) multiplying cut length by the unit weight (kg/m) to get weight per bar; (3) multiplying weight per bar by number of pieces to get total weight for that bar mark; (4) summing all bar marks. For example, 50 bars of 12mm diameter at 4.2m each: weight = 50 × 4.2 × (12² ÷ 162) = 50 × 4.2 × 0.888 = 186.5 kg. Add all bar marks and apply a wastage factor of 3–5% (for CTL bars) or 5–7% (for site-cut bars from standard 12m lengths) to get the order weight.

IS 1786:2008 Table 3 specifies the following tolerance on nominal mass (unit weight): for bars 6mm to 10mm diameter, ±7%; for bars 12mm and above, ±5%. This means a 20mm bar with a nominal weight of 2.469 kg/m may legitimately weigh between 2.346 kg/m and 2.592 kg/m and still comply with IS 1786. In practice, reputable manufacturers supply bars close to nominal weight. Under-weight bars (at the lower tolerance limit) deliver less steel per tonne than nominal — if ordering by weight and not by number of bars and length, short-weight bars effectively reduce the structural steel quantity in the building. Always verify bar weight on delivery for large structural orders.

Both 6mm and 8mm bars are used for stirrups and ties in residential RCC construction. 6mm stirrups are used for lightly loaded beams and columns — typically secondary beams and columns in structures up to two floors. 8mm stirrups are the standard for primary beams and columns in residential construction (up to 5 floors). IS 456:2000 Clause 26.5.3.2 requires that lateral ties in columns must not be less than one-quarter of the largest longitudinal bar diameter or 6mm — whichever is greater. For a column with 20mm main bars, the minimum tie diameter is 20 ÷ 4 = 5mm, so 6mm is technically adequate, but 8mm is standard practice for better workability and corrosion resistance.

The number of bars per tonne depends on diameter and bar length. For standard 12m bars: 6mm bars — approximately 148 bars per tonne (each weighs 6.75 kg); 8mm bars — approximately 84 bars per tonne (11.84 kg each); 10mm bars — approximately 54 bars per tonne (18.5 kg each); 12mm bars — approximately 38 bars per tonne (26.6 kg each); 16mm bars — approximately 21 bars per tonne (47.4 kg each); 20mm bars — approximately 14 bars per tonne (74.1 kg each); 25mm bars — approximately 9 bars per tonne (115.8 kg each); 32mm bars — approximately 5 bars per tonne (190.4 kg each). These counts are useful for planning crane lifts, storage areas, and delivery schedule — each bundle of a given size occupies a predictable space and can be lifted with a standard construction crane.