Gravel & aggregate
Area = 30.00 m²; finished volume = 1.500 m³
1.500 m³ × 1 compaction × 1.05 waste = 1.575 m³ loose
1.575 m³ × 1.60 t/m³ = 2.52 t
Waste, delivery & cost
How it's calculated
rectangle L × W · circle π d² / 4 · triangle b × h / 2V = Σ(area × depth × quantity)V_loose = V × compaction factor × (1 + waste %)M = V_loose × loose densitytons = tonnes × 1000 / 907.185area per tonne = 1 / (depth × compaction × density)bags = M × 1000 / bag mass (or V_loose / bag volume)⌈ M / payload ⌉The finished volume is the area times the depth you want after the layer is spread and compacted. Loose material takes more room than the finished layer, so the volume is multiplied by a compaction factor (1 for decorative gravel that is only raked level, about 1.15 for sub-base that is rolled or plated) and by an allowance for waste. Weight is the loose volume times the loose bulk density, which is the density of the material as delivered. A tonne is 1000 kg; a US ton is 2000 lb (907 kg). For a bed of sand or stone under a slab, see theconcrete calculator; for garden walls, thebrick and block calculator.
Worked example: a sub-base path
A path 6 m long and 1 m wide, with 100 mm of finished MOT Type 1 sub-base. Loose density 1.90 t/m³, compaction factor 1.15, 10% waste.
| Step | Working | Result |
|---|---|---|
| Area | 6 × 1 | 6.00 m² |
| Finished volume | 6 × 0.100 | 0.600 m³ |
| With compaction | 0.600 × 1.15 | 0.690 m³ |
| With 10% waste | 0.690 × 1.10 | 0.759 m³ |
| Weight | 0.759 × 1.90 | 1.44 tonnes |
For decorative gravel the compaction factor is 1: a driveway 10 m by 3 m at 50 mm deep is 1.5 m³, which at 1.6 t/m³ is 2.4 tonnes before waste. In US units, a patio 20 × 10 ft with 3 in of crushed stone is 50 ft³ (1.85 yd³), or about 2.5 tons.
Assumptions
- Densities are typical loose, dry bulk densities from merchant and estimating sites. They vary with the rock, the grading and especially moisture: wet gravel and sand weigh more. Use your supplier's figure when you have it, and edit the density field.
- The compaction factor is a rule of thumb. 1.15 is common for sub-base; some guides use 1.10 to 1.30.
- Depth is the finished depth. For uneven ground, enter an average depth.
- Waste covers spillage and over-depth only. Compaction is a separate factor.
- A layered build, such as 150 mm of sub-base under 50 mm of gravel, is two calculations: run the calculator once per layer, or add a second area with its own depth and material.
- Digging out is covered by the excavation calculator. Geotextile and edging are not included.
Frequently asked questions
How much does a tonne of gravel cover?
About 12.5 m² at 50 mm deep, using 1.6 t/m³ (1 / (0.05 × 1.6)). At 25 mm it covers about 25 m²; at 100 mm, about 6 m². In US units, a ton covers about 100 ft² at 2 in deep.
How many bags of gravel do I need?
Work out the weight first, then divide by the bag weight. One tonne is 50 bags of 20 kg or 40 bags of 25 kg. For the sub-base path above, 1.44 tonnes is about 72 bags of 20 kg. Bulk bags are sold by weight or volume, so enter the bag size you will buy in the calculator and it counts the bags for you.
How many tonnes are in a cubic metre of gravel?
About 1.6 for loose gravel and crushed stone. Sub-base such as MOT Type 1 is about 1.9 loose and 2.1 to 2.2 once compacted. Sharp sand is about 1.6 and building sand about 1.5 when dry.
How many tons are in a cubic yard of gravel?
About 1.35 to 1.4 US tons for typical gravel and crushed stone, which is a loose density of 1.6 to 1.65 t/m³. Conversion: tons per yd³ = t/m³ × 0.843.
How deep should gravel be?
Decorative gravel and paths usually take 40 to 50 mm (about 2 in). A driveway is often 50 mm of gravel over 100 to 150 mm of compacted sub-base. Heavier traffic needs a designed sub-base.
How much extra should I allow for compaction?
None for decorative gravel that is only raked. For sub-base that is rolled or plated, 10 to 15% extra is the usual allowance, which is a compaction factor of 1.10 to 1.15.
What is MOT Type 1?
A well-graded crushed stone sub-base mix specified in the UK Specification for Highway Works (clause 803). In the US, crusher run or dense-graded aggregate base (ABC) is used in a similar way.
Standards and references
- BS EN 13242: aggregates for unbound and hydraulically bound materials for use in civil engineering work.
- BS EN 12620: aggregates for concrete.
- Specification for Highway Works, Series 800, clause 803 (Type 1 unbound mixture).
- ASTM C29/C29M: bulk density and voids in aggregate.
- ASTM D448: sizes of aggregate for road and bridge construction (for example #57 stone).
These documents define the materials and the test methods. The densities used here are typical values, not values from the standards. This calculator estimates quantities only. It does not design a sub-base or check bearing capacity. Have the design checked by a qualified engineer.