By Tim King · Updated 16 September 2026

Gravel Calculator

Cubic Metres or Yards to Tonnes, With Waste Allowance and Bag Count

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Units

Material

Length (metres)

Width (metres)

Depth (e.g. 100mm)

Waste allowance (%, 10 if left blank)

Result

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How the Gravel & Sand Calculator works

This gravel calculator works out the volume and tonnes of gravel or sand to order. Put in the length, width and depth of the area, pick the material, and the volume and weight appear as you type — in cubic metres or cubic yards, and in tonnes, which is how quarries and landscape yards actually sell it. A 10% waste allowance is added unless you change it. Depths take units, so 75mm, 3in and 0.1 all work.

The formula. Volume = length × width × depth, plus 10% for waste and settling; tonnes = volume × density, about 1.6 t/m³ for gravel. For example, a 3 × 3 m area at 50 mm is 0.45 m³, 0.50 m³ with waste, or 0.79 tonnes. A second example: 5 × 4 m at 75 mm is 1.5 m³, 1.65 m³ with waste, or 2.64 tonnes. Divide the weight by 20 kg to see how many bags that would be.

Gravel calculator: area × depth, then convert to weight

The volume of a gravel bed is simply length × width × depth, with all three in the same unit. The trap is the depth: it is nearly always measured in millimetres or inches while the area is in metres or feet, and dropping the conversion produces an order a thousand times out. This page reads the unit with the number, so you can type the depth the way it is written on the plan.

Volume is only half the answer because bulk material is sold by weight. Converting needs the bulk density of the loose material, and that is where most online figures go wrong: they quote the density of the rock itself, which is around 2.7 t/m³, rather than the density of a loose pile of it with air between the pieces. The loose figures used here are 1.6 t/m³ for crushed rock and gravel, 1.5 for dry sand, 1.7 for damp sand and road base, and 1.2 for lightweight scoria. They match what suppliers use to convert an order, so the tonnage on this page is the tonnage you ask for.

Why sand gets heavier when it rains

Damp sand is listed separately because water adds weight without adding volume. Sand that has sat in a yard through a wet week can be 10 to 15% heavier than the same sand dry. If you are buying by the tonne, that difference is money; if you are buying by the cubic metre, it is not. Ask which way the yard sells before you compare quotes.

The assumed waste allowance is 10%

No excavated bed is a perfect rectangle. Edges are ragged, the base undulates, and some material is lost in the barrow and on the path. The default 10% covers a flat, prepared area. Push it to 15% for a sloping or hand-dug site, and to 20% if the material is going to be compacted: road base and crusher dust compact by 10 to 15% under a plate compactor, so the finished depth is thinner than the loose depth you spread. For a path or driveway base that must end up at 100mm compacted, spread 115mm loose or increase the allowance to match.

How deep should the layer be?

A decorative gravel mulch over weed mat needs 40 to 50mm — deep enough to hide the fabric, shallow enough that it does not shift underfoot. A path or patio base wants 75 to 100mm of compacted road base. A driveway that will carry cars needs 150mm of compacted base under the finished surface. A sandpit is 200 to 300mm deep. Bedding sand under pavers is 25 to 30mm.

Bags versus bulk

The 20kg bag count is for small jobs. A cubic metre of gravel is about 80 bags, which is not a sensible thing to carry from a hardware store; beyond about a quarter of a cubic metre, a bulk delivery or a trailer load from a landscape yard is cheaper and far less work. Yards typically sell in half-cubic-metre or half-tonne increments, so round up to the next one.

Gravel by area at 50 mm deep

Gravel or crushed rock at 1.6 t per m³, 50 mm deep, with 10% waste.

Volume, tonnes and 20 kg bags of gravel by area at 50 mm

Area	Volume	Tonnes	20 kg bags
2 × 2 m	0.22 m³	0.35 tonnes	about 18
3 × 2 m	0.33 m³	0.53 tonnes	about 27
3 × 3 m	0.50 m³	0.79 tonnes	about 40
4 × 2 m	0.44 m³	0.70 tonnes	about 36
4 × 3 m	0.66 m³	1.06 tonnes	about 53
4 × 4 m	0.88 m³	1.41 tonnes	about 71
5 × 3 m	0.83 m³	1.32 tonnes	about 67
5 × 4 m	1.10 m³	1.76 tonnes	about 89
5 × 5 m	1.38 m³	2.20 tonnes	about 110
6 × 3 m	0.99 m³	1.58 tonnes	about 80
6 × 4 m	1.32 m³	2.11 tonnes	about 106
6 × 5 m	1.65 m³	2.64 tonnes	about 133
6 × 6 m	1.98 m³	3.17 tonnes	about 159
7 × 4 m	1.54 m³	2.46 tonnes	about 124
7 × 5 m	1.93 m³	3.08 tonnes	about 155
8 × 4 m	1.76 m³	2.82 tonnes	about 141
8 × 5 m	2.20 m³	3.52 tonnes	about 177
8 × 6 m	2.64 m³	4.22 tonnes	about 212
10 × 4 m	2.20 m³	3.52 tonnes	about 177
10 × 5 m	2.75 m³	4.40 tonnes	about 220
10 × 6 m	3.30 m³	5.28 tonnes	about 265

FAQ

How much gravel do I need for a 10 square metre area?

At 50mm deep, 10 m² is 0.5 m³ of geometry, or 0.55 m³ with 10% waste. Crushed rock at 1.6 t/m³ makes that about 0.9 tonnes, so order one tonne. Each extra 50mm of depth adds another 0.55 m³ and roughly another 0.9 tonnes.

How many tonnes is a cubic metre of gravel?

About 1.6 tonnes for loose crushed rock or gravel, 1.5 for dry sand or pea gravel, and 1.7 for damp sand or road base. Decorative scoria is much lighter at around 1.2 t/m³. These are loose bulk densities, not the density of the solid rock, which is what a supplier uses to price a load.

What waste allowance does this calculator use?

Ten per cent by default, added to the calculated volume before converting to tonnes and bags. Raise it to 15% for sloping or hand-dug areas, and to around 20% for road base or crusher dust that will be compacted, because compaction reduces the loose depth by roughly that much.

How deep should gravel be for a driveway or path?

A driveway that carries cars needs about 150mm of compacted road base under the finished surface. A garden path or patio base needs 75 to 100mm. Decorative gravel over weed matting only needs 40 to 50mm, and bedding sand under pavers is 25 to 30mm.

Can I convert cubic yards of gravel to tons?

Yes, and the imperial mode does it. One cubic yard is 0.765 m³, so a yard of crushed rock at 1.6 t/m³ weighs about 1.22 tonnes, or 1.35 US short tons. Supplier figures of "1.3 to 1.4 tons per yard" are quoting the same density in US tons.

How many 20kg bags of gravel are in a cubic metre?

About 80, since 1 m³ of loose gravel weighs roughly 1,600 kg. Bags make sense for a few square metres at most; above a quarter of a cubic metre, a trailer load or a bulk delivery from a landscape yard is cheaper per tonne and saves a great deal of lifting.