Construction calculator

Gravel Calculator

Area length (m)Area width (m)Layer depth (m)Bulk density (kg/m³)

Required material (kg): -

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Calculation explained

How this result was calculated

The formula, your substituted values, and the evaluated result are shown below.

This is a planning estimate. Confirm dimensions, allowances, material specifications, applicable codes, and supplier requirements before purchasing or construction.

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How the Gravel Calculator works

Estimate gravel quantity from area, depth, and bulk density.

Before using the result

This is a planning estimate. Confirm dimensions, allowances, material specifications, applicable codes, and supplier requirements before purchasing or construction.

About this calculator

Estimate gravel quantity from area, depth, and bulk density.

Calculator guide

How the gravel calculator works

Gravel, crushed rock and road base are sold by the tonne but spread by volume, so this calculator does both steps at once. It works out the volume of the layer, then multiplies by the material's bulk density to give a weight:

Material (kg) = length (m) × width (m) × depth (m) × bulk density (kg/m³)

Divide the answer by 1,000 to get tonnes, which is how most landscape yards quote.

Worked example: a 5 m × 3 m gravel pad

Length 5 m, width 3 m, depth 75 mm = 0.075 m
Volume: 5 × 3 × 0.075 = 1.125 m³
Bulk density for typical 20 mm crushed gravel: about 1,600 kg/m³
1.125 × 1,600 = 1,800 kg, or 1.8 tonnes

If you will compact the layer with a plate compactor, allow roughly 10–20% more material, because compaction squeezes out the air gaps. For this pad I'd order about 2.1 tonnes.

Typical bulk densities

Material	Approx. loose bulk density
Pea gravel / river pebble	1,500 – 1,700 kg/m³
Crushed rock (10–20 mm)	1,500 – 1,650 kg/m³
Road base / crusher dust	1,700 – 2,000 kg/m³
Washed sand	1,500 – 1,700 kg/m³

These vary with moisture and the quarry, so ask your supplier for the figure they use. Most will tell you straight away. Using their number means your order matches their scales.

How deep should the layer be?

Decorative topping over an existing base: 40–50 mm
Garden paths: 50–75 mm over a compacted base
Driveways: usually 100–150 mm of compacted road base, with a 40–50 mm topping on top

A thin layer on soft ground ruts quickly. On a driveway, the compacted base does the structural work, not the decorative stone.

Common mistakes

Entering depth in millimetres. 75 mm must be entered as 0.075.
Using the density of solid rock (about 2,600 kg/m³) instead of the loose bulk density. That overestimates by more than half.
Forgetting the compaction allowance on road base.

Frequently asked questions

How many tonnes of gravel are in a cubic metre?

For most gravels, about 1.5 to 1.7 tonnes per cubic metre loose.

How much area does one tonne of gravel cover?

At 50 mm deep and 1,600 kg/m³, one tonne covers about 12.5 m². At 75 mm deep it covers about 8.3 m².

Should I lay weed mat under gravel?

For decorative gravel, yes. A permeable geotextile stops the stone sinking into the soil and cuts down on weeds. For driveways, a heavy-duty geotextile under the base helps on clay or soft ground.

Written by Sam Alex, civil engineer. About the author