Mulch Calculator
Work out how much mulch a bed or border needs — from the area and depth, in cubic yards and bags, with your own bag size.
Mulch is bought by the bag but needed by the cubic yard — and the link is the depth. This calculator turns the bed size and the depth into a volume and a bag count.
Measure the bed, pick the depth, and enter the bag size from the packaging.
Your results
Enter your measurements and press Calculate.
Quantities are rounded up to whole tiles, planks, boxes or bags, after the wastage allowance. Cost appears only when you enter a price.
Formula
All lengths are converted to a single unit before the calculation: 1 ft = 0.3048 m, 1 in = 25.4 mm, 1 ft² = 0.09290304 m², 1 yd² = 9 ft². Material quantities are rounded up — you cannot buy part of a tile, plank or bag.
How to use this calculator
- Choose the shape of the area (rectangle, circle, or a known area).
- Enter the depth — 2–4 in is normal for mulch.
- Enter the bag volume from the packaging.
- Add a price per bag if you want a cost estimate.
Worked example
| Bed | 10 ft × 20 ft |
|---|---|
| Area | 10 × 20 = 200 ft² |
| Volume (3 in deep) | 200 × 0.25 ft = 50 ft³ = 1.85 yd³ |
| With 10% wastage | 50 × 1.10 = 55 ft³ = 2.04 yd³ |
| Bags (2 ft³ bags) | ⌈55 ÷ 2⌉ = 28 bags |
Check it by hand: every step above uses the formula in the box. If your numbers match the example inputs but the calculator gives a different answer, please report it via the contact page.
Frequently asked questions
How deep should mulch be?
2–4 in (50–100 mm) is standard. Less than 2 in does not suppress weeds; more than 4 in can smother roots and hold too much water. This calculator defaults to 3 in.
How many bags of mulch do I need?
Divide the volume by the bag volume and round up. A 10 × 20 ft bed at 3 in deep needs 2.04 yd³ — 28 bags of 2 ft³. Enter your own bag size above; bags differ by supplier.
Does mulch settle?
Yes — fresh mulch settles by about 10–20% in the first few weeks. The 10% wastage allowance covers this; top up after a month if needed.
What is the difference between mulch and compost?
Mulch sits on top of the soil to keep moisture in and weeds down. Compost is mixed into the soil to feed it. Use the compost calculator for compost.
Related calculators
Estimates only. Results are for planning. Measure twice, confirm box coverage and tile sizes on the packaging you buy, and follow the manufacturer's instructions. See the disclaimer.