MOT Type 1 Coverage Calculator(Compacted Sub-Base Coverage)

Estimate MOT Type 1 sub-base coverage.

Calculate MOT Type 1 coverage per tonne at 100mm, 150mm, or 200mm with compaction allowance.

🕒 Last updated: August 20, 2026

Inputs

Gravel Type

Bulk Density (kg/m³)

ℹ️Auto-filled by material. Replace with supplier-tested density when available.

Target Area

Depth / Thickness

Bag Size for Results

▾

Quantity to Order (incl. 5% wastage)

17.21 tonnes

17,207 kg

15% compaction allowance included

Number of Bags

689 bags

21 × 850kg bulk bags

Rounded up to complete bags

Material: MOT Type 1 / Crusher Run

Density: 1,900 kg/m³

Wastage: 5% included

Coverage Visualizations

Coverage Area

Layer Depth Cross-Section

Practical Coverage at 150.0mm Depth

After 5% wastage and 15% compaction allowance

1 × 25kg bag

0.1 m²

1 × 850kg bulk bag

2.5 m²

1 tonne

2.9 m²

2 tonnes

5.8 m²

Your quantity

50.0 m²

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MOT Type 1 order quantity for a finished base

MOT Type 1 is a dense compactable sub-base, not a decorative loose gravel.

The defaults apply 15% compaction to a 150mm finished layer.

Representative density: 1,900kg/m³.
Compaction should follow the project specification.
Calculate surface gravel separately.

How Is Gravel Coverage Calculated?

Gravel coverage is calculated from area, depth, density, and wastage allowance. The calculation first converts the required layer into a volume, then converts that volume into mass using the selected gravel density.

Step 1 — Convert depth to metres

Depth (m) = Depth (mm) ÷ 1,000

Depth must be in metres before calculating volume. For example, a 50 mm gravel layer is 50 ÷ 1,000 = 0.05 m deep.

Step 2 — Calculate gravel volume

Volume (m³) = Area (m²) × Depth (m)

If a path area is 20 m² and the gravel depth is 50 mm, the depth is 0.05 m. The volume is therefore 20 × 0.05 = 1.00 m³.

Step 3 — Convert volume into mass

Mass (kg) = Volume (m³) × Bulk Density (kg/m³)

Gravel is commonly sold by weight. If the volume is 1.00 m³ and the selected gravel density is 1,600 kg/m³, the base quantity is 1.00 × 1,600 = 1,600 kg, or 1.60 tonnes.

Step 4 — Add wastage when calculating order quantity

Order Mass = Base Mass × (1 + Wastage ÷ 100)

Wastage covers spreading loss, edge migration, settlement, uneven ground, and handling loss. If the base quantity is 1,600 kg and wastage is 10%, order mass = 1,600 × 1.10 = 1,760 kg.

Step 5 — Reduce coverage when quantity is fixed

Usable Coverage Area = Supplied Mass ÷ [Density × Depth × (1 + Wastage ÷ 100)]

When you already have a fixed quantity, wastage reduces the practical area it can cover. For example, 1,000 kg of gravel at 1,500 kg/m³ and 50 mm depth covers 13.33 m² before wastage, but only about 12.12 m² with a 10% allowance.

Step 6 — Calculate achievable depth from quantity and area

Depth (m) = Supplied Mass ÷ [Area × Density × (1 + Compaction ÷ 100) × (1 + Wastage ÷ 100)]

This mode is useful when you already have a bulk bag and want to know how thick the layer will be. Compaction and wastage reduce the achievable depth the same way they reduce coverage area in Step 5 — for example, 850 kg of gravel at 1,450 kg/m³ over 11.15 m² gives about 52.6 mm before any allowance, or about 47.8 mm with a 10% wastage allowance included. After calculating depth in metres, multiply by 1,000 to convert the result back to millimetres.

Worked Gravel Coverage Examples

The examples below show how to enter real site measurements into the gravel coverage formula. Each example lists the calculator inputs first, then applies the same formula steps used by the calculator: convert depth, calculate volume, convert volume to mass using bulk density, and apply wastage or compaction allowance where required.

Formula reminder: use FIND QUANTITY when area and depth are known, FIND AREA when quantity and depth are known, and FIND DEPTH when quantity and area are known. The core formulas are: Volume = Area × Depth, Mass = Volume × Density, and Order Mass = Base Mass × (1 + Allowance ÷ 100).

Example 1 — Calculate Gravel Required for a Garden Path

Calculator mode: FIND QUANTITY

A homeowner wants to build a decorative garden path that is 12 m long and 0.8 m wide. The selected gravel is golden flint with an assumed loose bulk density of 1,500 kg/m³. The gravel layer will be 40 mm deep, and a 10% wastage allowance is added for spreading loss, edge migration, and settlement.

Input details

These are the values the user would enter or select in the calculator before reading the result.

Input	Value	Why it matters
Calculator mode	FIND QUANTITY	Use this mode when the area and depth are known, and the calculator must find how much gravel to order.
Material	Golden flint / decorative gravel	Use the matching gravel type or manually enter density.
Bulk density	1,500 kg/m³	This converts gravel volume into weight.
Length	12 m	Used to calculate path area.
Width	0.8 m	Used to calculate path area.
Depth	40 mm	Decorative path layer thickness.
Wastage	10%	Allows for spreading loss and later settlement.
Bag size	850 kg bulk bag	Used to convert final quantity into bags.

Step-by-step calculation

The table below shows how the input values are placed into the formula and converted into the final result.

Step	Formula / Substitution	Result
Calculate area	Area = Length × Width	12 × 0.8 = 9.60 m²
Convert depth to metres	Depth (m) = Depth (mm) ÷ 1,000	40 ÷ 1,000 = 0.04 m
Calculate gravel volume	Volume = Area × Depth	9.60 × 0.04 = 0.384 m³
Convert volume to mass	Mass = Volume × Density	0.384 × 1,500 = 576 kg
Add wastage	Order Mass = Base Mass × 1.10	576 × 1.10 = 633.6 kg
Convert to tonnes	Tonnes = kg ÷ 1,000	633.6 ÷ 1,000 = 0.63 tonnes
Convert to bulk bags	Bags = Order Mass ÷ Bag Size	633.6 ÷ 850 = 0.75 bag → order 1 bulk bag

Result

The path requires about 634 kg, or 0.63 tonnes, of decorative gravel. Since gravel is commonly delivered in 850 kg bulk bags, one bulk bag is sufficient, with spare material for topping up after settlement.

Practical note

For paths, edging is important. Without edging, gravel spreads into the lawn or soil border, reducing the effective depth and increasing future top-up quantity.

Example 2 — Calculate Driveway Surface Gravel Quantity

Calculator mode: FIND QUANTITY

A driveway is 5 m wide and 8 m long. The owner wants a 50 mm loose surface layer using 20 mm granite gravel. The assumed loose bulk density is 1,600 kg/m³. A 10% allowance is added for spreading, settlement, and small surface irregularities.

Input details

These are the values the user would enter or select in the calculator before reading the result.

Input	Value	Why it matters
Calculator mode	FIND QUANTITY	Use this mode when the driveway area and required surface depth are known.
Material	20 mm granite gravel	Dense decorative or driveway surface gravel.
Bulk density	1,600 kg/m³	Granite is denser than slate or pea gravel.
Length	8 m	Driveway length.
Width	5 m	Driveway width.
Depth	50 mm	Loose driveway surface gravel layer.
Wastage	10%	Allows for spreading loss, uneven level, and settlement.
Bag size	1,000 kg bulk bag / tonne bag	Useful for ordering.

Step-by-step calculation

The table below shows how the input values are placed into the formula and converted into the final result.

Step	Formula / Substitution	Result
Calculate area	Area = Length × Width	8 × 5 = 40.00 m²
Convert depth to metres	Depth (m) = Depth (mm) ÷ 1,000	50 ÷ 1,000 = 0.05 m
Calculate volume	Volume = Area × Depth	40.00 × 0.05 = 2.00 m³
Convert volume to mass	Mass = Volume × Density	2.00 × 1,600 = 3,200 kg
Add wastage	Order Mass = Base Mass × 1.10	3,200 × 1.10 = 3,520 kg
Convert to tonnes	Tonnes = kg ÷ 1,000	3,520 ÷ 1,000 = 3.52 tonnes
Convert to 1-tonne bags	Bags = Order Mass ÷ 1,000	3,520 ÷ 1,000 = 3.52 bags → order 4 tonne bags if bags are the only option

Result

The driveway surface layer requires about 3.52 tonnes of 20 mm granite gravel. If the supplier delivers only full 1-tonne bags, round up to 4 bags. If loose bulk delivery is available, order close to 3.5 tonnes plus supplier rounding.

Practical note

This example calculates only the loose surface gravel layer. A driveway normally also needs a compacted sub-base such as crusher run, MOT Type 1, or GSB. Calculate the sub-base separately because it uses different density, depth, and compaction assumptions.

Example 3 — Check How Much Area One Bulk Bag Covers

Calculator mode: FIND AREA

A user already has one 850 kg bulk bag of river gravel and wants to know how much area it will cover at 50 mm depth. The assumed loose bulk density is 1,450 kg/m³. A 10% practical allowance is included to avoid spreading the gravel too thin.

Input details

These are the values the user would enter or select in the calculator before reading the result.

Input	Value	Why it matters
Calculator mode	FIND AREA	Use this mode when the available gravel quantity and required depth are known, and the calculator must find coverage area.
Material	River gravel	Rounded natural gravel used for gardens and decorative areas.
Bulk density	1,450 kg/m³	Used to convert the 850 kg bag into volume.
Quantity	850 kg	One standard bulk bag.
Depth	50 mm	Target finished gravel thickness.
Wastage / allowance	10%	Reduces practical coverage area.

Step-by-step calculation

The table below shows how the input values are placed into the formula and converted into the final result.

Step	Formula / Substitution	Result
Convert quantity to kg	Supplied Mass = 850 kg	850 kg
Calculate available volume	Volume = Mass ÷ Density	850 ÷ 1,450 = 0.586 m³
Convert depth to metres	Depth (m) = Depth (mm) ÷ 1,000	50 ÷ 1,000 = 0.05 m
Coverage before wastage	Coverage = Volume ÷ Depth	0.586 ÷ 0.05 = 11.72 m²
Apply wastage allowance	Usable Coverage = Base Coverage ÷ 1.10	11.72 ÷ 1.10 = 10.65 m²

Result

One 850 kg bulk bag of river gravel covers about 11.7 m² at 50 mm depth before wastage. With a 10% practical allowance, use about 10.6 m² as the safer coverage estimate.

Practical note

This is why many suppliers say one bulk bag covers roughly 10–12 m² at 50 mm depth. The exact value depends on gravel density, moisture, grading, and how evenly the material is spread.

Example 4 — Check Achievable Depth from a Fixed Quantity

Calculator mode: FIND DEPTH

A user has one 850 kg bulk bag of gravel and wants to spread it over a 10 ft × 12 ft patio border. Instead of asking how much area the bag covers, the question is: what depth will this bag achieve over the known area?

Input details

These are the values the user would enter or select in the calculator before reading the result.

Input	Value	Why it matters
Calculator mode	FIND DEPTH	Use this mode when the gravel quantity and area are known, and the calculator must calculate achievable depth.
Material	River gravel	Assumed loose density of 1,450 kg/m³.
Bulk density	1,450 kg/m³	Used to convert mass into volume.
Quantity	850 kg	One bulk bag.
Area	10 ft × 12 ft	Area must be converted to m² before using the formula.
Wastage / allowance	10%	Used to estimate practical depth after settlement and spreading loss.

Step-by-step calculation

The table below shows how the input values are placed into the formula and converted into the final result.

Step	Formula / Substitution	Result
Calculate area in ft²	Area = Length × Width	10 × 12 = 120 ft²
Convert area to m²	Area (m²) = Area (ft²) × 0.092903	120 × 0.092903 = 11.15 m²
Calculate available volume	Volume = Mass ÷ Density	850 ÷ 1,450 = 0.586 m³
Calculate depth in metres	Depth = Volume ÷ Area	0.586 ÷ 11.15 = 0.0526 m
Convert depth to mm	Depth (mm) = Depth (m) × 1,000	0.0526 × 1,000 = 52.6 mm
Apply 10% allowance	Practical Depth = Base Depth ÷ 1.10	52.6 ÷ 1.10 = 47.8 mm

Result

One 850 kg bulk bag spread over a 10 ft × 12 ft area gives about 53 mm depth before wastage, or about 48 mm practical depth with a 10% allowance.

Practical note

This example is useful when the user already has material on site and wants to know whether it is enough for the intended area.

Example 5 — Estimate MOT Type 1 for a Driveway Sub-Base

Calculator mode: FIND QUANTITY

A small driveway sub-base is 4 m wide and 6 m long. The required compacted thickness is 150 mm. MOT Type 1 / crusher run is assumed at 1,900 kg/m³ loose bulk density. A 15% allowance is used to account for compaction and small level variations.

Input details

These are the values the user would enter or select in the calculator before reading the result.

Input	Value	Why it matters
Calculator mode	FIND QUANTITY	Use this mode when the sub-base area and depth are known, and the calculator must find the order quantity.
Material	MOT Type 1 / crusher run	Dense graded sub-base material with fines.
Bulk density	1,900 kg/m³ loose	Loose density used for ordering estimate.
Length	6 m	Driveway length.
Width	4 m	Driveway width.
Depth	150 mm	Target compacted sub-base thickness.
Compaction / allowance	15%	Allows for loose-to-compacted reduction and surface variation.

Step-by-step calculation

The table below shows how the input values are placed into the formula and converted into the final result.

Step	Formula / Substitution	Result
Calculate area	Area = Length × Width	6 × 4 = 24.00 m²
Convert depth to metres	Depth (m) = Depth (mm) ÷ 1,000	150 ÷ 1,000 = 0.15 m
Calculate compacted layer volume	Volume = Area × Depth	24.00 × 0.15 = 3.60 m³
Convert volume to mass	Base Mass = Volume × Density	3.60 × 1,900 = 6,840 kg
Add compaction allowance	Order Mass = Base Mass × 1.15	6,840 × 1.15 = 7,866 kg
Convert to tonnes	Tonnes = kg ÷ 1,000	7,866 ÷ 1,000 = 7.87 tonnes

Result

The driveway sub-base requires approximately 7.9 tonnes of MOT Type 1 / crusher run, assuming 150 mm compacted depth and a 15% allowance.

Practical note

For sub-base work, supplier density, compaction method, layer thickness, and project specification matter. Do not calculate compacted roadbase exactly the same way as loose decorative gravel.

Calculator Limitations & Assumptions

Bulk density is material-specific but not quarry-specific: Actual density varies by source quarry. For large areas (> 50 tonnes), ask your supplier for a tested bulk density and enter it using Custom.
Depth assumes uniform laying: The calculator assumes uniform depth across the entire area. Uneven ground increases effective material requirement.
Coverage area assumes rectangular calculation: For irregular shapes, break into sub-areas, calculate each, and sum totals. L-shaped and triangular areas can be entered using the Gravel Weight Calculator.
Compaction factors are typical ranges: Actual compaction depends on gradation, equipment, moisture, and passes. Set compaction to 0% for loose decorative gravel and open-graded drainage material, which must not be compacted.
Cost estimate excludes delivery and taxes: the estimate covers material cost only.

Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.

FAQ

MOT Type 1 is delivered and spread loose, then compacted to its finished thickness with a roller or plate compactor — without a 15-25% loose-material allowance, the finished layer falls short of the specified depth.

1,900 kg/m³ is a common representative value; this page defaults to it. Confirm with your supplier for large orders, since actual density varies by source and grading.

Yes for most driveways — MOT Type 1 is a structural sub-base, not a wearing surface. Calculate a separate top layer (gravel, asphalt, or pavers) with its own density and depth.

It depends on the gravel type and the depth you are laying it. For typical garden gravel such as pea gravel or decorative granite chip at 50mm depth, 1 tonne covers approximately 12–14m². At 40mm depth, the same tonne covers 15–17m². At 25mm depth, it covers 25–28m². The reference table shows coverage per tonne for every major gravel type at five standard depths.

A standard UK bulk bag holds approximately 850kg, although some are marketed as 1,000kg, so check with your supplier. At 50mm depth, 850kg of typical garden gravel covers approximately 10–12m² depending on material density. At 40mm depth, coverage extends to 13–15m². The calculator gives the precise figure for the selected material.

For decorative garden borders and around plants, 30–40mm is adequate. For garden paths with foot traffic, 50mm is the recommended minimum. For driveways, use a 50–75mm decorative surface layer on top of a separate compacted sub-base. Never use a single loose gravel layer for driveways without a sub-base because it will displace under vehicle loading.

Enter the area and depth, then select the bag size. The calculator rounds up to whole bags and shows both small bags and bulk bags. As a quick guide, a 25kg bag of typical garden gravel at 50mm depth covers approximately 0.31–0.33m², while an 850kg bulk bag covers approximately 10–12m².

MOT Type 1 at about 1,900kg/m³ is much denser than garden gravel. At 100mm depth, 1 tonne covers approximately 5.3m² before loose-material compaction allowance. For a 5m × 8m driveway at 150mm compacted depth, the approximate order is 40 × 0.15 × 1.9 × 1.20 = 13.68 tonnes. Use a project-specific compaction factor for structural sub-base ordering.

Calculate the area as π × radius², then use the coverage formula. For a circular garden bed with a 3m diameter, area = π × 1.5² = 7.07m². At 50mm of pea gravel, the requirement is 7.07 × 0.05 × 1,500 = approximately 530kg before wastage.

FIND QUANTITY answers 'how much gravel do I need?' from a known area and depth. FIND AREA answers 'how far will this gravel go?' from a known quantity and depth. FIND DEPTH answers 'how thick a layer can I achieve?' from a known quantity and area — useful when material is already on site or delivered.

Yes — turn on the Compaction Factor under Advanced Options for GSB, WMM, MOT Type 1, or crusher run, and set it to 0% for loose decorative gravel and open-graded drainage material, which must not be compacted.

Bulk density varies significantly by gravel type — MOT Type 1 (~1,900 kg/m³) is roughly 30% denser than pea gravel (~1,480 kg/m³), so using the wrong type's density can make a coverage estimate 20-30% wrong.

5% is reasonable for a machine-spread or carefully contained area. Increase to 8-12% for driveways (edge displacement, vehicle scatter), irregular or curved areas, and any hand-spread work without edging.