How to use the mulch calculator
- Measure your bed’s length and width, or enter the total area if you already know it. For curved beds, use the square footage calculator to add up circles and odd shapes first.
- Choose the depth. 2–3 inches (5–7.5 cm) suits most beds.
- Pick the bag size sold at your store to see how many bags to buy, or use the cubic yards or cubic metres figure to order loose (bulk) material.
The mulch formula
Volume = area × depth Cubic yards = cubic feet ÷ 27 Litres = cubic metres × 1,000 Bags = volume ÷ bag size (rounded up)
Depth must be in the same unit as the area: convert inches to feet by dividing by 12, or centimetres to metres by dividing by 100.
Worked example (US)
A 10 × 10 ft bed at 3 inches deep: 100 ft² × 0.25 ft = 25 ft³. That is 0.93 cubic yards, or 12.5 bags of 2 ft³ — so buy 13 bags.
Worked example (UK)
A 3 × 3 m border at 7.5 cm deep: 9 m² × 0.075 m = 0.675 m³, or 675 litres. That is 14 × 50 L bags or 10 × 70 L bags.
Recommended depths
| Use | US depth | UK depth |
|---|---|---|
| Flower beds and borders (mulch, bark) | 2–3 in | 5–7.5 cm |
| Weed suppression on bare ground | 3–4 in | 7.5–10 cm |
| Bark paths and play areas | 3–4 in+ | 7.5–10 cm+ |
| Compost top-dressing | 1–2 in | 2.5–5 cm |
| Topsoil for a new lawn | 4–6 in | 10–15 cm |
Play-area surfacing for safety needs specific depths for the fall height of the equipment; follow the manufacturer’s guidance for those.
Bags or bulk?
Bags are tidy and easy to carry, but expensive per cubic yard. Once you need more than about 1–2 cubic yards (roughly 1–1.5 m³), a bulk delivery is usually cheaper — in the UK, loose bark and topsoil often come in bulk bags of around 1 m³. Ask the supplier for the exact volume of their bulk bags, as they vary.
Frequently asked questions
How many bags of mulch are in a cubic yard?
A cubic yard is 27 ft³, so it takes 13.5 bags of 2 ft³ or 9 bags of 3 ft³. Bulk mulch by the yard is usually much cheaper than bags once you need more than a yard or two.
How much area does a yard of mulch cover?
One cubic yard covers about 108 ft² at 3 inches deep, 162 ft² at 2 inches or 324 ft² at 1 inch. In metric, 1 m³ covers about 13 m² at 7.5 cm deep or 20 m² at 5 cm.
How deep should mulch be?
For most beds and borders, 2–3 inches (5–7.5 cm) suppresses weeds and holds moisture. Go deeper on paths or very weedy ground. Keep mulch a few inches away from tree trunks and plant stems to prevent rot.
How many litres are in a bag of bark or compost?
UK garden centres commonly sell bark and compost in 50, 60, 70, 75 and 100 litre bags. A cubic metre is 1,000 litres, so you need 20 × 50 L bags or 10 × 100 L bags per m³.
Can I use this calculator for topsoil or compost?
Yes. The volume maths is the same for mulch, bark, compost, topsoil and soil improver. Loose topsoil settles once firmed, so add 10–20% extra when filling raised beds or levelling a lawn.