Offcut WorksGravel and aggregate calculator
Enter the area and depth. You get the volume and the weight to order, and the number of bulk bags. Change the density if your supplier gives a different figure.
How the numbers are worked out
Volume = area × depth. A 6 m × 4 m area at 50 mm is 24 × 0.05 = 1.2 m³.
Weight = volume × density. Add your extra for waste first, because the extra is spread, spilt and left in the bag. At 1.6 t/m³ and 10% extra, 1.2 m³ is 1.2 × 1.1 × 1.6 = 2.1 tonnes.
Bags = weight ÷ bag weight, rounded up.
Density changes the answer
Stone is sold by weight but laid by depth, so density matters. Dry decorative gravel is lighter than compacted MOT Type 1, and wet sand and soil are heavier than dry. If your supplier states a figure, enter it instead of the default.
Loose or compacted
Sub-base such as MOT Type 1 settles when compacted, so a layer laid at one depth ends up thinner. Enter the compacted depth you need and the density of the compacted material. Use the waste allowance for the rest, and ask your supplier how much they advise.
Choosing a depth
For sub-base under paving, see the patio calculator, where the depth is part of the build-up. Decorative gravel depths vary by use, and a weed-control membrane under the gravel is common. Check the gravel supplier's advice for your surface.
Bulk bags or loose loads
Bulk bags are easy to deliver to a small site and keep material dry, but cost more per tonne than a loose tipper load. For several tonnes, ask for a loose price too.
Questions
How do I convert cubic metres of gravel to tonnes?
Multiply the volume by the density. For decorative gravel at about 1.6 tonnes per cubic metre, 1 m³ is about 1.6 tonnes. Your supplier can give the exact density.
How much MOT Type 1 do I need?
Multiply the area by the compacted depth to get cubic metres, then by about 2.1 to get tonnes. Add a little extra for waste.
How many bulk bags is a tonne?
Bulk bags are often between 800 and 900 kg, so a tonne is a little more than one bag. Check the weight of the bag you buy.
Where the defaults come from
Show the 1 source
- UK supplier and calculator pages. Compacted Type 1 densities of about 2.0 to 2.2 tonnes per cubic metre, and bulk bags of about 800 to 900 kg (one retailer lists 850 kg).
- All the densities are typical values. We found Type 1 figures from 2.0 to 2.2 t/m³, but we did not find a standard that fixes them, and we did not find a primary source for gravel, sand or topsoil. Ask your supplier.
- The 850 kg bulk bag weight is one retailer's listing. Bags vary.
- The 10% waste is our own allowance.