How to use the mulch calculator
Measure the bed's length and width in feet, or the diameter of a round tree ring, and enter the depth you want. If the bed already has some mulch on it, enter that depth under Already there and the calculator only counts the top-up. The result shows bulk cubic yards and bag counts for the three common bag sizes.
The same math works for compost, garden soil and topsoil sold by the bag or the yard; only the depth changes.
The formula
- Cubic feet = area (sq ft) × depth (in) ÷ 12
- Cubic yards = cubic feet ÷ 27
- Bags = cubic feet ÷ cubic feet per bag, rounded up
- Round bed: area = 3.1416 × (diameter ÷ 2)²
How far a yard or a bag goes
| Depth | 1 cubic yard covers | 1.5 cu ft bag covers | 2 cu ft bag covers | 3 cu ft bag covers |
|---|---|---|---|---|
| 1 in | 324 sq ft | 18 sq ft | 24 sq ft | 36 sq ft |
| 2 in | 162 sq ft | 9 sq ft | 12 sq ft | 18 sq ft |
| 3 in | 108 sq ft | 6 sq ft | 8 sq ft | 12 sq ft |
| 4 in | 81 sq ft | 4.5 sq ft | 6 sq ft | 9 sq ft |
Mulch for common bed sizes
At 3 inches deep:
| Bed | Sq ft | Cubic yards | 1.5 cu ft bags | 2 cu ft bags | 3 cu ft bags |
|---|---|---|---|---|---|
| 10 × 4 ft | 40 | 0.37 | 7 | 5 | 4 |
| 20 × 3 ft | 60 | 0.56 | 10 | 8 | 5 |
| 20 × 10 ft | 200 | 1.85 | 34 | 25 | 17 |
| 30 × 6 ft | 180 | 1.67 | 30 | 23 | 15 |
| 50 × 4 ft | 200 | 1.85 | 34 | 25 | 17 |
How deep to mulch
| Where | Depth |
|---|---|
| Top-up on an existing bed | 1 to 2 in |
| Beds on heavy (clay) soil | 2 to 3 in |
| Beds and tree rings, well-drained soil | 3 to 4 in |
| Paths and play areas (wood chips) | 3 to 4 in, more for play areas per the surfacing maker |
More isn't better. Mulch piled too deep keeps soil wet and starves roots of air, and mulch heaped against a trunk (a "mulch volcano") invites rot and rodents.
Worked examples
A tree ring
An 8 ft circle around a young tree at 3 in: area 3.1416 × 4² = 50.3 sq ft, volume 12.57 cu ft, so 7 bags of 2 cu ft. Leave a bare ring around the trunk itself.
Topping up
300 sq ft of beds that still have about 1 1/2 in of old mulch, brought back to 3 in: only 1 1/2 in is new, so 37.5 cu ft = 1.39 yd³. Measuring the old layer first can halve the order.
Bags or bulk?
A cubic yard is 13.5 bags of 2 cu ft or 9 bags of 3 cu ft. Past about 2 cubic yards, bulk mulch from a landscape yard is usually much cheaper per yard, even with delivery. Bags make sense for small beds, for keeping the driveway clean, and when you want a specific dyed or bagged product.
Questions people ask
How many bags of mulch do I need for 100 sq ft?
At 3 in deep, 100 sq ft takes 25 cu ft: 13 bags of 2 cu ft or 9 bags of 3 cu ft.
How many square feet does a yard of mulch cover?
162 sq ft at 2 in, 108 sq ft at 3 in and 81 sq ft at 4 in.
Does mulch settle?
Fresh, fluffy mulch settles and breaks down over the season. Many gardeners apply a little extra, or plan a 1 in top-up each year.