Mulch Calculator (Cubic Yards and Bags)
Enter the bed size and the depth you want to estimate bulk mulch in cubic yards or the number of bags.
How it works
Cubic yards = area (sq ft) × depth (in) ÷ 324, because one cubic yard covers 324 sq ft one inch deep (27 cu ft × 12). Cubic feet = area × depth (in) ÷ 12. Bags = cubic feet ÷ bag size, rounded up.
Worked examples
- Iowa State Extension's example: a 265 sq ft bed at 1.5 inches needs 265 × 1.5 ÷ 12 = 33.1 cu ft = 1.23 cu yd, or 17 bags of 2 cu ft.
- Tree ring 8 ft across at 3 in: π × 4² = 50.3 sq ft × 3 ÷ 12 = 12.6 cu ft (0.47 cu yd), or 7 bags of 2 cu ft. Keep the mulch back from the trunk (see below), so the real need is a little less.
- Border bed 30 × 4 ft at 2 in: 120 × 2 ÷ 324 = 0.74 cu yd (20 cu ft), or 7 bags of 3 cu ft.
How to measure
- Measure the length and width of each bed. For a round bed or tree ring, measure across the widest point.
- Split curved beds into rectangles and circles, or find the square footage with the square footage calculator or an online map tool (Iowa State Extension mentions these).
- Measure any old mulch already there and subtract it from the depth you want.
Common mistakes
- Piling mulch against tree trunks ("mulch volcanoes"). Prairie View A&M Extension says never to let mulch touch the trunk and to leave about 3 inches of space all around.
- Spreading it too deep. Extension guidance is about 2 to 4 inches, with fine mulch kept thinner.
- Forgetting existing mulch, which adds to the depth.
- Mixing up bag sizes. Bags are sold as 1.5, 2 or 3 cu ft; a cubic yard is 27 cu ft, or 13.5 two-cubic-foot bags.
Assumptions
- Even depth across the whole bed. Plants, rocks and edging are not subtracted.
- Bag sizes are the labeled volume; mulch may settle after spreading.
- Depth is your choice. Iowa State Extension says many hardwood mulches are spread 2 to 4 inches thick; Prairie View A&M Extension suggests about 2 inches of organic mulch, no more than 3 inches for fine textures and up to 4 for coarse.
- The waste allowance is an editable JobsiteCalc default, not an industry standard. Ask your supplier what extra they suggest for your job.
Frequently asked questions
How much area does a cubic yard of mulch cover?
Prairie View A&M Extension: one cubic yard covers 324 sq ft at 1 inch, 162 at 2 inches, 108 at 3 inches and 81 at 4 inches.
How many bags of mulch do I need?
Divide the cubic feet needed by the bag size. Iowa State Extension's example: 265 sq ft at 1.5 inches needs 33.1 cu ft, or 17 two-cubic-foot bags (1.22 cubic yards).
How deep should mulch be?
Extension services commonly cite 2 to 4 inches, with finer mulch kept thinner. Mulch that is too deep can keep water and air from reaching the soil.
Related calculators
- Topsoil calculator – to fill or top-dress the bed before mulching
- Square footage calculator – for odd-shaped beds
- Gravel calculator – for stone mulch and paths
- Fill dirt calculator – to raise low spots before you plant and mulch
- Sod and grass seed calculator – for the lawn around the beds
Sources
Formulas and reference values are from these sources. Page content last updated 2026-10-19.