Plot No. 67 · Home & Garden
Gravel Calculator
Work out how much gravel an area needs by weight. It multiplies length by width by depth to get the volume in cubic metres, multiplies that by the gravel density to get tonnes, then divides by the weight of a bulk bag to give the number of bags to order.
A bulk bag is treated as roughly 0.85 tonnes and bag counts are rounded up. Stone densities vary, so adjust the density figure to match your chosen gravel.
The link saves your inputs so you can bookmark or share this exact result.
How the gravel quantity is worked out
The calculator multiplies area length by width by depth to get the volume in cubic metres, converting the depth from centimetres to metres. Unlike mulch or soil, gravel is sold by weight, so the volume is then multiplied by the stone density in tonnes per cubic metre to give the tonnage.
Most decorative gravels sit around 1.6 tonnes per cubic metre, which is the default you can adjust for your stone. The tonnage is divided by 0.85, the weight of a standard bulk bag, and rounded up to give the number of bags to order.
How to use the gravel calculator
- Enter the area length and width in metres.
- Set the depth in centimetres, with about 5 cm suiting a decorative top layer.
- Adjust the density to match your gravel, then read off the tonnes and the number of bulk bags.
Worked examples
Decorative gravel area
Inputs: 5 m by 3 m area, 5 cm deep, density 1.6 tonnes per cubic metre
Result: 0.75 cubic metres, 1.2 tonnes of gravel, which rounds up to two bulk bags.
Deeper driveway top layer
Inputs: 5 m by 3 m area at 8 cm deep, same density
Result: 1.2 cubic metres and about 1.92 tonnes, which is three bulk bags once rounded up.
Limitations and common mistakes
Edge cases and limitations
- A bulk bag is treated as 0.85 tonnes, but real bags vary, so confirm the weight with your supplier.
- Densities differ by stone type and how wet it is, so adjust the density figure rather than trusting the default blindly.
- A gravel driveway carrying vehicles needs a deeper compacted sub-base beneath this top layer, which is not included.
Common mistakes
- Ordering by volume alone and ignoring density, then under-buying because gravel weighs more than expected.
- Spreading the layer too thin to save money, so the membrane shows through and weeds find the gaps.
Frequently asked questions
How much gravel do I need?
Multiply area by depth, then by density. A 5 m by 3 m area at 5 cm deep is 0.75 cubic metres. At 1.6 tonnes per cubic metre that is 1.2 tonnes, which is two bulk bags.
How deep should a gravel layer be?
Around 5 cm suits a decorative top layer over a membrane. A gravel driveway that takes vehicle weight needs more, often 5 cm of gravel over a deeper compacted sub-base, so increase the depth for traffic.
How much does a bulk bag of gravel weigh?
A standard bulk bag holds roughly 0.85 tonnes, which is why this tool divides your total tonnage by 0.85 to give the bag count. Densities vary by stone type, so 1.6 tonnes per cubic metre is a typical starting point you can adjust.
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