How much mulch, soil or gravel do I need?
Short answer: cubic yards = square feet × depth in inches ÷ 12 ÷ 27. A 10 by 20 foot bed mulched 3 inches deep needs 50 cubic feet. That is about 1.85 cubic yards, or 25 bags of 2 cubic feet each. Enter your own bed below.
1. Your bed or path
Suggested depth. Iowa State Extension: 3 to 4 inches of wood chips or shredded bark on well-drained sites, 2 to 3 inches on heavy soils. Keep it at least 6 inches from tree trunks.
2. How much to buy
- Cubic yards
- 1.85
- Cubic feet
- 50.0
- Bags
- 25
For bulk delivery
200.0 sq ft at 3.0 in deep
2 cu ft bags, rounded up
How this is calculated
- Area: length × width, or 3.1416 × (diameter ÷ 2)² for a circle.
- Cubic feet = square feet × depth in inches ÷ 12.
- Cubic yards = cubic feet ÷ 27, since a cubic yard is 3 × 3 × 3 feet.
- Bags = cubic feet ÷ bag size, rounded up to a whole bag.
- Gravel weight uses a supplier range of 1.3 to 1.7 tons per cubic yard. Ask your yard for the figure for the stone you buy. We do not show weight for mulch or soil because it varies too much with moisture.
The formula, step by step
- Find the area in square feet. Multiply length by width. For a circle, use 3.1416 × radius × radius. For odd shapes, split them into rectangles and add them up.
- Turn depth into feet. Divide inches by 12. Three inches is 0.25 feet.
- Multiply area by depth in feet to get cubic feet.
- Divide by 27 to get cubic yards. A cubic yard is 3 feet × 3 feet × 3 feet.
As a check, the University of Maryland Extension says 1 inch of compost over 1,000 square feet takes 3 cubic yards. The formula gives 3.09 cubic yards for the same job.
Worked examples
| Job | Area | Depth | Cubic feet | Cubic yards | 2 cu ft bags |
|---|---|---|---|---|---|
| Mulch a 10 × 20 ft bed | 200 sq ft | 3 in | 50 | 1.85 | 25 |
| Mulch ring, 6 ft across | 28.3 sq ft | 3 in | 7.1 | 0.26 | 4 |
| Gravel path, 3 × 30 ft | 90 sq ft | 3 in | 22.5 | 0.83 | 12 |
| Topsoil a 4 × 8 ft raised bed | 32 sq ft | 6 in | 16 | 0.59 | 8 |
Bags are rounded up to a whole bag. At a supplier range of 1.3 to 1.7 tons per cubic yard, the gravel path weighs about 1.1 to 1.4 tons.
How deep to spread mulch
- Around trees and shrubs: Iowa State Extension suggests 3 to 4 inches of wood chips or shredded bark on well-drained sites. On heavy soils, use 2 to 3 inches.
- Keep it off the trunk. Iowa State says to keep mulch at least 6 inches from tree trunks. Mulch piled against bark can lead to fungal cankers, root rot and rodent damage.
- No mulch volcanoes. Mississippi State Extension warns against mounding mulch up around the trunk. It suggests a 3 to 4 inch layer that extends 3 to 6 feet around the tree.
Shredded leaves make free mulch. See whether to rake or mulch your leaves andhow to compost in a small yard.
Bulk or bags?
One cubic yard is 27 cubic feet. That equals 13.5 bags of 2 cubic feet, 18 bags of 1.5 cubic feet or 9 bags of 3 cubic feet. Bags are easy to carry and fine for small beds. For bigger jobs, compare the price of a delivered cubic yard with 13.5 bags. Ask about the delivery fee and any minimum order before you decide.
Check the bag label. Bag sizes are listed in cubic feet, and a 1.5 cubic foot bag covers less than you might expect. At 3 inches deep, it covers 6 square feet.
Common questions
How many bags of mulch are in a yard?
A cubic yard holds 13.5 bags of 2 cubic feet. Buy 14 bags if you need a full yard from 2 cubic foot bags.
How much area does one cubic yard cover?
At 3 inches deep, one cubic yard covers 108 square feet. At 2 inches, it covers 162 square feet.
How deep should a gravel path be?
A gravel supplier guide suggests 2 to 3 inches for light foot traffic. Use 3 to 4 inches for paths that carry carts or wheelbarrows.
Should I add extra for settling?
Loose materials settle and fill low spots, so many people round up. The calculator already rounds bags up. For bulk, round up to the next half or whole yard your supplier sells.
Does this work for compost?
Yes. The math is the same for any loose material. Before topdressing a lawn, read when to fertilize your lawn.