Gravel Calculator
Calculate the gravel, aggregate or crushed stone needed for a driveway, path or base layer, by volume and weight.
How to use this calculator
- 1Measure the area. For an irregular space, split it into rectangles, work each out, and add them.
- 2Set the unit you measured in — the calculator converts everything for you.
- 3Check the coverage figure against the bag or tin you are actually buying; it varies between brands.
- 4Leave the waste allowance on. Running short mid-job costs far more than one spare unit.
How the calculation works
Units = ⌈ (Area × Depth × (1 + waste)) / Volume per unit ⌉- Area
- Surface area of the job
- Depth
- How thick the material is laid
- waste
- Allowance for cuts, breakage and spillage
- ⌈ ⌉
- Round up — you cannot buy a fraction of a unit
Every dimension is converted to metres internally, so feet, yards and metres can be mixed with inches or centimetres without error.
Gravel is sold by weight but laid by volume, so density is the bridge between the two. Loose gravel runs 1.4–1.7 tonnes per cubic metre depending on stone size and moisture.
Worked example
A 20 × 12 ft area
- 1.20 ft × 12 ft = 240 sq ft, which is 22.30 m².
- 2.At the depth set above, that gives the volume shown in the result.
- 3.A 5% waste allowance is added, then the figure is rounded up to whole tonnes.
Result: See the result panel — it updates live as you change the numbers.
What gravel and aggregate actually are
"Gravel" covers a wide range of loose stone products, from rounded pea gravel to angular crushed stone, generally somewhere between about 2 mm and 65 mm across. It gets used loose — a decorative bed, a drainage layer — or compacted in layers as a sub-base under a driveway or path, and the right type depends heavily on which of those two jobs it is doing.
Unlike concrete, gravel doesn’t cure or bond into a solid mass on its own — it relies on compaction, particle size, and sometimes a geotextile fabric underneath to stay stable and drain properly. That’s also why it settles over time: rolling and rain both work loose material down into a denser layer than it occupied the day it was delivered.
Common types of gravel and aggregate
- Crushed stone / crusher run — angular, mechanically crushed rock, often sold as a mix of sizes down to dust. The angularity locks together well under compaction, which makes it the standard choice for a driveway sub-base.
- Pea gravel — small, smooth, rounded stones, comfortable underfoot and popular for pathways and decorative beds, but it doesn’t compact or lock together as firmly as crushed stone.
- River rock — larger, smooth, rounded stone used mostly for drainage swales and decorative borders rather than a walkable or driveable surface.
- Decomposed granite — fine, crushed granite that compacts into a firm, natural-looking surface, often used for paths and low-traffic parking areas.
- Road base — a graded mix specifically designed for sub-base layers under driveways, patios and paved surfaces, sized to compact densely with minimal voids.
Layering a gravel driveway or path
A gravel surface that will carry any real weight is normally built up in layers rather than dumped in one go.
- 1Excavate to the required depth — deep enough for every layer plus any edging or geotextile fabric, with the topsoil and organic material removed so nothing underneath continues to compress later.
- 2Lay a geotextile membrane — a permeable fabric that stops the gravel working its way down into the soil beneath, and stops weeds working their way up.
- 3Add and compact the sub-base — a coarser crushed stone layer, spread and mechanically compacted — this is the layer doing most of the structural work.
- 4Top with the finish layer — a finer or more decorative gravel spread over the compacted base to the final depth.
Where estimates commonly go wrong
- Ignoring compaction — gravel measured loose in a pile settles noticeably once spread and rolled — often 10–15% — so a delivery that looked generous can fall short once it’s compacted to final depth.
- Using one density figure for every stone type — density varies with stone size and moisture; a supplier’s actual tonnage-per-cubic-metre figure for the specific product is more reliable than a generic rule of thumb on a large order.
- Skipping the sub-base — a thin layer of decorative gravel laid straight onto soil will sink, rut, and need topping up constantly wherever vehicles or heavy foot traffic cross it.
What this assumes, and where it stops
Assumptions
- The area is flat and regular as described. Slopes, steps and obstructions change the quantity.
- Coverage figures are the manufacturer’s stated values, which assume good conditions and an even surface.
- A density of roughly 1.6 tonnes per cubic metre unless you change the coverage figure.
Limitations
- This estimates material only — not labour, tools, delivery, hire or disposal.
- Manufacturer coverage varies between brands and batches. Always check the packaging.
- Density varies by stone type and moisture content. Ask your supplier for their figure on large orders.
- Does not include the geotextile membrane or sub-base most driveways need beneath the gravel.
Common questions
How deep should gravel be?
About 2 inches (50 mm) for a footpath, 3–4 inches (75–100 mm) for a decorative area, and 4–6 inches (100–150 mm) of sub-base plus a top layer for a driveway that will carry vehicles.
How much does a tonne of gravel cover?
At 50 mm deep, roughly 12–13 m² (about 130 sq ft). At 100 mm deep it halves to around 6 m². The calculator works this out from the depth you enter.
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
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