Mulch, Soil & Gravel Calculator (cubic yards and bags)
Work out the mulch, topsoil, sand, or gravel a bed needs by area and depth — in cubic yards, bags, or tons.
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Cubic yards by area and depth
Bags in brackets are 2 ft³ bags — the common bagged mulch size.
| Bed area | 1 in deep | 2 in deep | 3 in deep | 4 in deep | 6 in deep |
|---|---|---|---|---|---|
| 50 ft² | 0.154 yd³ (3) | 0.309 yd³ (5) | 0.463 yd³ (7) | 0.617 yd³ (9) | 0.926 yd³ (13) |
| 100 ft² | 0.309 yd³ (5) | 0.617 yd³ (9) | 0.926 yd³ (13) | 1.23 yd³ (17) | 1.85 yd³ (25) |
| 200 ft² | 0.617 yd³ (9) | 1.23 yd³ (17) | 1.85 yd³ (25) | 2.47 yd³ (34) | 3.7 yd³ (50) |
| 400 ft² | 1.23 yd³ (17) | 2.47 yd³ (34) | 3.7 yd³ (50) | 4.94 yd³ (67) | 7.41 yd³ (100) |
| 800 ft² | 2.47 yd³ (34) | 4.94 yd³ (67) | 7.41 yd³ (100) | 9.88 yd³ (134) | 14.8 yd³ (200) |
| 1000 ft² | 3.09 yd³ (42) | 6.17 yd³ (84) | 9.26 yd³ (125) | 12.3 yd³ (167) | 18.5 yd³ (250) |
Materials, depths and weights
| Material | Bulk density | Typical depth | 1 yd³ weighs | 1 yd³ covers |
|---|---|---|---|---|
| Bark mulch | 400 kg/m³ | 3 in | 0.306 t | 108 ft² |
| Wood chips | 500 kg/m³ | 3 in | 0.382 t | 108 ft² |
| Compost | 700 kg/m³ | 2 in | 0.535 t | 162 ft² |
| Topsoil | 1300 kg/m³ | 4 in | 0.994 t | 81 ft² |
| Sand | 1600 kg/m³ | 2 in | 1.22 t | 162 ft² |
| Pea gravel | 1700 kg/m³ | 2 in | 1.3 t | 162 ft² |
| Crushed stone | 1600 kg/m³ | 4 in | 1.22 t | 81 ft² |
Bulk densities are for loose, reasonably dry material. Wet soil and wet bark are considerably heavier.
Working out mulch, soil and gravel
Every one of these is the same sum: the area of the bed times how deep you want it. The awkward part is that the two measurements are in different units — the bed is in feet or metres, the depth in inches or centimetres — and the answer is wanted in cubic yards, which is a third unit again.
Volume = area × depth · 1 cubic yard = 27 cubic feet
Worked example
A 20 × 5 ft border is 100 ft². At the usual 3 inch mulch depth that is 100 × 0.25 = 25 ft³, and since a cubic yard is 27 ft³, just under one yard — or 13 bags of the 2 ft³ bagged stuff. That comparison is worth making every time: 13 bags is often more expensive and always more lifting than a single bulk yard tipped on the drive.
How deep should it go?
Bark mulch wants 2–3 inches. Less and weeds come through; much more and you risk keeping the soil too wet and starving roots of air, especially piled against stems. Compost as a top dressing is 1–2 inches. Topsoil for a new lawn is 4–6 inches of usable depth. Gravel paths want 2–3 inches over a compacted base, and a driveway considerably more, in layers. The calculator starts each material at its typical depth.
Bags or bulk?
The crossover is usually around half a cubic yard — roughly seven 2 ft³ bags. Below that, bags are easier to handle and you can buy exactly what you need. Above it, bulk is cheaper per yard, and by the time you are at two or three yards the difference is substantial. The catch is delivery: bulk arrives as a pile where the truck can reach, and moving three tonnes of wet topsoil by barrow is a real day's work.
Why weight matters
Suppliers often sell aggregates by the ton rather than the yard, and the two are not interchangeable between materials — a cubic yard of bark is around 0.3 tonnes while the same volume of gravel is over 1.3. Check which one you are being quoted. Weight also decides whether your vehicle can carry it: a cubic yard of wet topsoil comfortably exceeds the payload of a small trailer.
Related
For a bed made of several rectangles and curves, total the area first with the area calculator. For a hard base under a path, the concrete calculator covers the poured layer.
Bulk density moves with moisture
The volume is exact; the weight is not. Bulk densities for loose material are representative figures for reasonably dry product, and moisture changes them substantially — wet topsoil and wet bark are considerably heavier than the table suggests. That matters when a supplier sells by the ton rather than the yard, and when you are deciding whether a vehicle can legally carry the load. Settlement is a second factor: loose material compacts after laying, so a bed finished at the target depth will sit lower in a few weeks.