Mulch Calculator
How much mulch your beds need in cubic yards or cubic metres, and how many bags to buy.
Your bed
Filled in with example values. Replace them with your own.
Optional
Adds a percentage on top of the measured volume.
Bag sizes vary between brands. Use the volume printed on the bag you plan to buy.
Results update as you type.
Result
Mulch needed: 0.741 yd³
You need about
0.741cubic yards
- Volume in cubic feet
- 20 ft³
- Volume in cubic metres
- 0.566 m³
- Area covered
- 80 ft²
- Bags
- Turn on “Count bags”
How it’s calculated
Area
20 ft × 4 ft = 80 ft²
Volume
80 ft² × 0.25 ft deep = 20 ft³
In cubic yards
20 ft³ ÷ 27 = 0.741 yd³
How the mulch calculator works
Mulch is sold by volume: in bags marked in cubic feet or litres, or loose by the cubic yard or cubic metre. The calculator treats your bed as a rectangle covered to an even depth, converts all measurements to the same unit and multiplies length × width × depth.
If you add an allowance, it goes on top of that volume. If you turn on bag counting and enter the volume printed on your bags, the calculator divides the total by the bag size and rounds up to whole bags.
The formula
Volume = Length × Width × Depth
Volume with extra = Volume × (1 + Extra % ÷ 100)
Bags = Volume with extra ÷ Volume per bag, rounded up
Bed sizes are usually measured in feet or metres but mulch depth in inches or centimetres, so convert depth first: 3 inches is 3 ÷ 12 = 0.25 feet, and 7.5 centimetres is 0.075 metres.
Worked example
A border bed is 20 feet long and 4 feet wide, and you want mulch 3 inches deep. The bags you plan to buy say 2 cubic feet on the label.
- Depth in feet: 3 ÷ 12 = 0.25 ft
- Area: 20 ft × 4 ft = 80 ft²
- Volume: 80 ft² × 0.25 ft = 20 ft³
- In cubic yards: 20 ÷ 27 = 0.74 yd³
- Bags: 20 ft³ ÷ 2 ft³ = 10 bags
In metric: a bed 5 m long, 2 m wide and 7.5 cm deep needs 5 × 2 × 0.075 = 0.75 m³, which is 750 litres. If your bags hold 50 litres, that is 750 ÷ 50 = 15 bags.
Units, assumptions and limitations
- Conversions use exact definitions: 1 inch = 2.54 cm, 1 foot = 12 inches, 1 yard = 3 feet, 1 litre = 0.001 m³.
- The bed is treated as a flat rectangle with an even depth. Curves, slopes and plants in the bed change the real amount.
- No bag size is assumed. Brands and countries use different sizes, so enter the one on your label.
- The result is the volume of mulch in place. Allow extra if you expect it to settle or if the ground is uneven.
Frequently asked questions
How many bags of mulch are in a cubic yard?
Divide 27 (the cubic feet in a cubic yard) by the bag size. For 2 cubic foot bags that is 27 ÷ 2 = 13.5, so you would buy 14 bags. For 3 cubic foot bags it is exactly 9.
Why are bags rounded up?
You can only buy whole bags, and rounding down would leave part of the bed uncovered. The calculator always rounds up to the next whole bag.
How deep should mulch be?
It depends on the mulch and what it is for, such as suppressing weeds or keeping soil moist. Check the advice for your plants and your mulch, then enter that depth here.
Can I use this for compost, topsoil or bark?
Yes. The calculation is the same for any loose material spread to an even depth: length × width × depth. Only the name on the bag changes.
How do I measure a curved or round bed?
Split an irregular bed into rectangles, calculate each one and add them up. For a round bed, the area is 3.1416 × radius × radius; a rectangle with the same area gives the same volume.
How many litres are in a cubic foot?
One cubic foot is about 28.32 litres, and one cubic metre is exactly 1,000 litres. The calculator converts between them for you, so you can enter the bag size in whichever unit is printed on it.