Landscaping Materials Volume Calculator
Enter area dimensions and depth to get the volume in cubic metres, litres, and tonnes. Shows bulk bag counts at 0.5m³, 0.75m³, and 1m³ bag sizes. Nothing uploaded.
Area & Depth
Material Required
Bulk bag sizes
Learn more: why bulk material weight varies so much
From volume to weight
The calculator multiplies length, width and depth to get a volume, then multiplies by a density for the chosen material to estimate tonnes. Its densities are 1.5 t/m3 for gravel, 1.8 for hardcore or MOT Type 1, 1.0 for topsoil, 1.6 for sand and for concrete ballast, 0.5 for compost and 0.3 for bark mulch.
The spread is why the same order differs so much by weight. 5 m3 of gravel is about 7.5 tonnes, while 5 m3 of bark mulch is about 1.5 tonnes. A 5 m x 3 m bed at 100 mm deep is 1.5 m3, so about 2.25 tonnes of gravel.
Densities are ranges, not fixed numbers
The squote guide to gravel quantities lists loose densities of 1.5 t/m3 for decorative gravel and 1.8 for MOT Type 1, matching the tool. It gives screened topsoil as 1.0 to 1.4 t/m3, which means the tool's 1.0 is at the light end, and building sand as 1.4, below the tool's 1.6.
Another converter, calculate.co.nz, lists loose topsoil at 1.2 and bark mulch at 0.7. Both sites say density depends on moisture, compaction and particle size. Treat the weight as an estimate, and ask your supplier for the figure for the product you are buying, especially if it is wet.
Compaction and bags
The calculator gives the volume you enter and adds nothing for settling. The squote guide says MOT Type 1 typically loses 8 to 15% of its volume when compacted and suggests ordering 10% extra for a sub-base. For decorative gravel, which is not compacted, it suggests a 5% allowance.
The bag counts divide volume by 0.5, 0.75 and 1.0 m3 and round up. Real bulk bags are often sold by weight. The same guide says bags marketed as 1 tonne typically hold 800 to 900 kg, so for dense material such as gravel, check the tonnes figure against the bag's weight too.
FAQ
Why does bark mulch weigh so much less than gravel?
Bark mulch is light organic material with lots of air between the pieces, while gravel is dense mineral aggregate. In the tool, bark is 0.3 t/m3 and gravel 1.5, so equal volumes differ by a factor of five.
How are the bag counts worked out?
It divides the volume by 0.5, 0.75 and 1.0 m3 and rounds up, since a part bag still means buying a whole one. These are volume bags. If your supplier sells bags by weight, compare the tonnes figure with the bag's stated weight.
Should I add extra for settling?
For a sub-base that will be compacted, the squote guide suggests about 10% extra, and about 5% for decorative gravel. The tool does not add this, so multiply the result yourself or increase the depth you enter.