Mulch and Soil Volume Calculator: Cubic Yards and Bags
Mulch and Soil Volume Calculator
Bed area and spread depth to cubic metres and cubic yards, the number of retail bags, and an approximate weight so the delivery, and the vehicle, can be planned honestly.
Bulk material is sold by the cubic yard in much of North America and by the cubic metre elsewhere; one cubic yard is 0.765 cubic metres, so a metre is about 1.31 yards and ordering the wrong one is a 31 percent error. Typical depths are 50 to 75 mm for decorative mulch, 75 to 100 mm for weed suppression, and 100 mm or more for a new bed. Densities are approximate and vary a lot with moisture.
How to use this tool
Bed dimensions, rectangular or circular, and a spread depth in millimetres. The tool returns the volume in both cubic metres and cubic yards, the number of retail bags, and an approximate weight for the material you pick.
The cubic yard is where the money goes wrong
Bulk landscape material is sold by the cubic yard across much of North America and by the cubic metre nearly everywhere else, and the two are not close: a cubic metre is 1.31 cubic yards. Order 3 cubic metres when you meant 3 cubic yards and 31 percent more material arrives than the bed can take. The tool prints both figures side by side for exactly this reason.
Weight matters for a different reason: the vehicle. Mulch is light, around 400 kilograms per cubic metre, but topsoil is roughly 1300 and gravel about 1600. Two cubic metres of gravel is over 3 tonnes, well past what a half-ton pickup should be carrying, and that is a delivery decision to make before ordering rather than in the yard. Densities vary considerably with moisture, so treat them as planning figures.
A worked check you can repeat on paper
A bed 5 by 4 metres is 20 square metres. At 75 millimetres deep the volume is 20 times 0.075, which is exactly 1.5 cubic metres, or 1.96 cubic yards. In 56 litre bags that is 1500 divided by 56, which is 26.8, so 27 bags. As bark mulch it weighs about 600 kilograms; as topsoil, 1.95 tonnes. Same hole, very different delivery.
Mistakes that catch people out
Ordering metres for yards or the reverse. A 31 percent error in whichever direction hurts. Fix: both units are printed together.
Spreading too thick or too thin. Under 50 millimetres of mulch does not suppress weeds; much over 100 around stems holds moisture against the plant. Fix: 50 to 75 millimetres decorative, 75 to 100 for weed suppression.
Buying bags for a bulk-sized job. Twenty-seven bags is a lot of plastic and usually dearer than a bulk load. Fix: compare the bag count against a bulk delivery once you pass a cubic metre or so.
Forgetting settlement. Loose mulch settles; soil compacts more. Fix: order at the depth you want after settling, and expect soil to need a little extra.
How this was checked
The volume arithmetic was verified on the worked example, the cubic yard conversion against the exact definition of 0.764554857984 cubic metres per cubic yard, and the bag count tested at the boundary so an exact fit returns no spare bag. The weight figures follow directly from the selected density.
Related Calculators and Reference
Bed areas in other shapes are the 2D Area Calculator, and volume conversions beyond yards and metres are the Volume Unit Converter. For a bed edged in concrete, quantities are the Concrete Mix Volume and Quantity Estimator. Seeding the new topsoil is the Grass Seed Calculator. Turfing the area instead of seeding it is the Sod Calculator. Feeding the lawn afterwards is the Fertilizer Calculator.