How much mulch do I need?
Volume (cu ft) = area (sq ft) × depth (in) ÷ 12
Cubic yards = cubic feet ÷ 27 · Bags = cubic feet ÷ bag size
Bulk mulch, topsoil and compost are sold by the cubic yard (27 cu ft); bagged mulch is usually 2 cu ft per bag. The same calculation works for any loose material spread at an even depth, so use it for topsoil, compost, garden soil and bark too.
Worked example: a 20 × 10 ft flower bed
- Area: 20 × 10 = 200 sq ft.
- At 3 in deep: 200 × 3 ÷ 12 = 50 cu ft, which is 1.85 cu yd (1.42 m³).
- In 2 cu ft bags: 50 ÷ 2 = 25 bags. Bulk, order 2 cu yd.
A tree ring 6 ft across
Area: π × 3² = 28.27 sq ft. At 3 in deep: 7.07 cu ft, so 4 bags of 2 cu ft. Keep mulch a few inches away from the trunk itself.
How deep should mulch be?
| Material | Typical depth |
|---|---|
| Fine mulch, shredded bark | 2–3 in (5–8 cm) |
| Coarse wood chips | 3–4 in (8–10 cm) |
| Topping up existing mulch | 1–2 in |
| Topsoil for new lawn or sod | 4–6 in (10–15 cm) |
| Compost worked into beds | 1–3 in |
University extension services generally recommend 2 to 4 in of organic mulch for beds and around trees, and warn against piling it against trunks ("mulch volcanoes"), which can cause rot and attract pests. Too thick a layer can also keep water and air from the roots.
Coverage of one cubic yard
| Depth | One cubic yard covers |
|---|---|
| 1 in | 324 sq ft |
| 2 in | 162 sq ft |
| 3 in | 108 sq ft |
| 4 in | 81 sq ft |
| 6 in | 54 sq ft |
One cubic yard equals 13.5 bags of 2 cu ft. For large areas, bulk delivery is usually far cheaper per yard than bags, but check the delivery fee.
Irregular beds
Split curved or irregular beds into rectangles and circles and add the volumes, or measure the length along the middle of a curved strip and multiply by its average width. It is better to order slightly more: loose material settles, and topsoil compacts by roughly 10–20% after watering and rolling.
Step by step: ordering mulch
- Measure each bed's length and width, or the diameter of tree rings.
- Decide on the depth: 2–4 in for most mulch, less when topping up.
- Work out the volume and compare bag and bulk prices.
- Pull back old mulch from trunks and stems before spreading the new layer.
- Spread evenly and water lightly to settle it.
Metric example
A bed 6 × 3 m mulched 7.5 cm deep needs 6 × 3 × 0.075 = 1.35 m³, which is 1,350 litres or 27 bags of 50 litres.
Mulch, topsoil or compost?
- Mulch (bark, wood chips, straw) sits on top of the soil to keep moisture in, block weeds and moderate soil temperature. It is not dug in.
- Topsoil is used to fill low spots, build raised beds and prepare ground for a new lawn. It is spread thicker and compacts after watering.
- Compost improves the soil itself. It is usually spread 1–3 in thick and worked into the top few inches of a bed, or used as a thin top dressing on lawns.
All three are measured the same way, so this calculator works for each; just change the depth.
Common mistakes
- Treating inches as feet: 3 in is 0.25 ft. A 200 sq ft bed at 3 in is 50 cu ft, not 600.
- Confusing cubic feet and cubic yards when ordering in bulk. There are 27 cu ft in a cubic yard.
- Spreading too thick in the hope of fewer weeds. Beyond about 4 in, mulch can harm plants.
Frequently asked questions
How many bags of mulch do I need?
Multiply the area in square feet by the depth in inches, divide by 12, then by the bag size. A 200 sq ft bed at 3 in is 50 cu ft, so 25 bags of 2 cu ft.
How much area does a yard of mulch cover?
At 3 in deep, one cubic yard covers about 108 sq ft; at 2 in, 162 sq ft; at 4 in, 81 sq ft.
How many bags of mulch are in a yard?
13.5 bags of 2 cu ft, because a cubic yard is 27 cubic feet.
How much topsoil do I need for a lawn?
For a new lawn, 4–6 in is common. A 1,000 sq ft lawn at 4 in needs 333 cu ft, about 12.3 cu yd.
How many 50 litre bags of mulch do I need?
Multiply area in square metres by depth in centimetres and by 10 to get litres, then divide by 50. A 18 m² bed at 7.5 cm needs 1,350 litres, so 27 bags.
Sources
- University extension guidance on mulching (e.g. Penn State Extension, University of Minnesota Extension): 2–4 in of organic mulch, kept away from trunks.
- NIST Handbook 44 Appendix C: 1 cubic yard = 27 cubic feet = 0.764555 m³.
Last reviewed 20 October 2026. Results are estimates; see our disclaimer.