Mulch Calculator
Measure the bed, pick a depth, and get the answer in cubic yards and bags — so you buy once instead of making a second trip for four more bags.
How the mulch calculator works
Mulch is sold by volume — either loose by the cubic yard or bagged by the cubic foot. The conversion is a three-step calculation:
- Cubic feet = length (ft) × width (ft) × depth (ft). Convert depth from inches by dividing by 12.
- Cubic yards = cubic feet ÷ 27.
- Bags = cubic feet ÷ the bag size, rounded up.
Worked example
A 20 ft × 10 ft bed at 3 inches deep:
- 20 × 10 = 200 sq ft
- 3 in ÷ 12 = 0.25 ft
- 200 × 0.25 = 50 cubic feet
- 50 ÷ 27 = 1.85 cubic yards
- 50 ÷ 2 = 25 bags of 2 cu ft mulch
At that size, loose mulch by the yard is usually cheaper than 25 bags — and it takes about ten minutes to wheelbarrow instead of twenty minutes of cutting plastic.
Coverage by depth
| Depth | 1 cubic yard covers | 2 cu ft bags per 100 sq ft | Best for |
|---|---|---|---|
| 1 in | 324 sq ft | 4.2 | Refreshing colour on existing mulch |
| 2 in | 162 sq ft | 8.3 | Established beds, fine mulch |
| 3 in | 108 sq ft | 12.5 | Standard new bed depth |
| 4 in | 81 sq ft | 16.7 | Bare soil, heavy weed pressure |
Choosing a depth
Three inches is the working standard for a new bed: deep enough to block light from weed seeds, shallow enough that water still reaches the soil. Two inches is fine for topping up an existing bed that has not broken down completely.
Do not go past four inches. Deep mulch holds moisture against trunks and stems, which invites rot, and it can starve shallow roots of oxygen. Keep mulch pulled back two or three inches from the base of trees, shrubs and the house.
Frequently asked questions
How many bags of mulch are in a cubic yard?
13.5 bags of 2 cubic feet, or 9 bags of 3 cubic feet. Bagged mulch is usually sold in 2 cu ft bags, so a “yard” at the garden centre is about 13–14 bags.
How deep should mulch be?
2–3 inches for established beds and 3–4 inches on bare soil where you are fighting weeds. Anything over 4 inches risks holding too much moisture against stems and suffocating shallow roots.
How much does a cubic yard of mulch cover?
108 square feet at 3 inches, 162 at 2 inches, 81 at 4 inches. If you only remember one figure, remember 108 at 3 inches.
Should I remove old mulch before adding new?
Not usually. Rake it to break up the crust, then top up to your target depth. Remove it if it has matted into a layer that sheds water, or if it is heavily contaminated with weeds or fungus.
How much does a cubic yard of mulch weigh?
Roughly 600–1,000 lb depending on material and moisture. Bark mulch is on the light end, hardwood and compost blends are heavier, and wet mulch can be 30% heavier than dry.