Mulch without the guesswork
Mulch keeps soil moist, holds back weeds and makes beds look finished, but it is easy to buy too much or run out halfway. The amount depends only on the area of your beds and how thick you spread it.
This mulch calculator gives the answer in cubic yards for a bulk delivery and in bags for the garden centre, for rectangular or round beds, with a metric mode in cubic metres and litres.
How to use it
- Measure each bed. For odd shapes, split them into rectangles and circles and add the results.
- Choose a depth. A layer of about 2 to 3 inches is common for beds; follow the advice for your plants and mulch.
- Pick your bag size, or the litres per bag in the metric mode.
- Read the cubic yards and the number of bags, rounded up to whole bags.
Keep mulch a few inches away from tree trunks and plant stems, where it can trap damp against the bark.
The mulch formula
area = length × width (circle: π × radius²)
cubic feet = area (ft²) × depth (in) ÷ 12
cubic yards = cubic feet ÷ 27
bags = cubic feet ÷ bag size, rounded upA cubic yard is a cube 3 feet on each side, so it holds 27 cubic feet. Mulch bags in the US are usually sold by the cubic foot, while bulk mulch is sold by the cubic yard.
Worked example: a 20 by 5 foot bed, 3 inches deep
- Area: 20 × 5 = 100 ft²
- Volume: 100 × 3 ÷ 12 = 25 cubic feet
- In cubic yards: 25 ÷ 27 = 0.93 cubic yards
- In 2 cubic foot bags: 25 ÷ 2 = 12.5, so 13 bags
The bed needs 0.93 cubic yards, or 13 bags of 2 cubic feet. For several beds that add up to a few cubic yards, a bulk load is usually cheaper than bags.
Coverage of one cubic yard
| Depth | Covers |
|---|---|
| 2 inches | 162 ft² |
| 3 inches | 108 ft² |
| 4 inches | 81 ft² |
To find coverage at any depth, divide 324 by the depth in inches. In metric, one cubic metre covers 10 square metres at 10 cm deep, and 20 square metres at 5 cm.
Bulk or bags?
Bags are easy to carry and store, and suit small jobs or topping up. Bulk mulch is delivered loose by the cubic yard or cubic metre, costs less per yard for larger jobs, but needs somewhere to tip it and a wheelbarrow to move it. Compare the two prices using the cubic yards above, and remember any delivery charge.
Related projects
- For stone paths and beds, use the gravel calculator.
- For new beds and lawns, the topsoil calculator works the same way.
- For a plain volume in any shape, see the cubic yard calculator.
Frequently asked questions
How much mulch do I need?
Multiply the bed length by its width in feet, then by the depth in inches, and divide by 12 to get cubic feet. Divide by 27 for cubic yards. A 20 by 5 foot bed at 3 inches deep needs 25 cubic feet, about 0.93 cubic yards, or 13 bags of 2 cubic feet.
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cubic feet, so it equals 13.5 bags of 2 cubic feet, 9 bags of 3 cubic feet, or 18 bags of 1.5 cubic feet. When buying bags, round up to whole bags. The calculator does this for the bag size you choose.
How deep should mulch be?
A layer of about 2 to 3 inches is a common choice for garden beds, deep enough to hold back weeds without smothering the soil. Very fine mulch can be thinner, and coarse bark a little thicker. Keep it pulled back from tree trunks and plant stems.
How much area does a bag of mulch cover?
A 2 cubic foot bag covers 12 square feet at 2 inches deep, or 8 square feet at 3 inches deep. To work it out, multiply the bag size in cubic feet by 12, then divide by the depth in inches. The calculator handles this for your whole bed.
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