Mulch calculator for cubic yards, bags and tons
Find how much mulch, gravel, topsoil or sand to buy for one bed or many.
Beds
Enter at least one bed to see how much you need.
Show the working
Conversion factors: NIST SP 811 Appendix B.8. Densities: see Sources below.
Extra and bags
Weight
This is an estimate. Volumes are exact for the shapes and depth you enter, but real beds are rarely perfect shapes, and mulch and soil settle. Weights use typical densities; your supplier's figure for their material is the one to trust. Check the volume printed on the bag before you buy.
Sources
- NIST SP 811, Appendix B.8: conversion factors (updated 2025-08-18)
- University of Illinois Extension, "Proper Mulching Techniques" (depth 2-4 in, 4 in from the trunk)
- USDA NRCS, "Soil Quality Indicators: Bulk Density" (topsoil and sand densities)
- NAVFAC DM-7 series, "Typical Properties of Compacted Materials" (gravel density)
- US EPA, MSW characterization Appendix D (wood chips about 500 lb per cubic yard)
- Scotts Nature Scapes product page (bag coverage check)
- Quikrete "Sand & Gravel Products" data sheet, rev. Nov 2020 (50 lb bags)
How it works
Add each bed as a rectangle, circle, tree ring, triangle or known area, then set a depth. The calculator multiplies area by depth, adds any extra you ask for, and converts the total to cubic yards, cubic feet, bags and tons. Every step appears in the "Show the working" panel under the result.
How we calculate it
These are the same steps, in the same order, as the panel under the result.
- Area of each bed:
- Rectangle: length × width
- Circle: π × (diameter ÷ 2)²
- Tree ring: π × (R² − r²), where R is half the outer diameter and r is half the trunk diameter plus the trunk gap (default 4 in)
- Triangle: base × height ÷ 2
- Known area: the area you enter
- Volume of each bed: sq ft × depth in inches ÷ 12 = cu ft. In metric, m² × depth in cm ÷ 100 = m³.
- Total: the bed volumes are added together.
- Extra: total × (1 + extra ÷ 100), if you set an extra percentage.
- Cubic yards: cu ft ÷ 27.
- Other units: cu ft × 0.0283168 = m³. In metric, m³ × 1,000 = litres, and m³ ÷ 0.764555 = cubic yards.
- Bags: cu ft ÷ bag size, rounded up to a whole bag. Sand and gravel bags are sold by weight, so their count is pounds ÷ bag weight (default 50 lb), rounded up.
- Weight: cubic yards × density in tons per cubic yard = short tons. × 2,000 = pounds. × 0.907185 = tonnes.
- Density used: the panel prints the figure and where it came from, or "entered by you" if you changed it.
- Coverage: 27 × 12 ÷ depth in inches = sq ft covered by one cubic yard.
| Material | Depth | Tons per yd³ | kg/m³ |
|---|---|---|---|
| Mulch | 3 in | 0.25 | 297 |
| Topsoil | 4 in | 1.12 | 1,330 |
| Sand | 2 in | 1.35 | 1,600 |
| Gravel | 3 in | 1.55 | 1,842 |
All maths uses unrounded values. Only the displayed numbers are rounded. Topsoil and sand weights are for dry material, and damp material weighs more. The gravel figure is the low end of a compacted range, so loose delivered gravel is often lighter. A compacted base needs more loose gravel than the volume shown. Unit factors come from NIST SP 811 Appendix B.8. The density sources are in the Sources list above.
Questions
How many bags of mulch are in a cubic yard?
A cubic yard is 27 cu ft. That is 18 bags of 1.5 cu ft, 13.5 bags of 2 cu ft, or 9 bags of 3 cu ft. Some brands, Scotts Nature Scapes among them, have cut their bag from 2 to 1.5 cu ft, so check the volume printed on the bag. Packaged mulch and soil are sold by that printed volume.
How do I work out how much gravel I need?
Multiply the area in square feet by the depth in feet (3 in is 0.25 ft), divide by 27 for cubic yards, then add about 10% for uneven ground. For 400 sq ft at 3 in that is 400 × 0.25 ÷ 27 × 1.1 = 4.07 cubic yards. Multiply by the weight per yard to get tons. At the default of 1.55 tons per yard that is 6.31 tons. Gravel weight varies with the stone, so ask your supplier for their figure and type it in.
How much area does a yard of mulch cover?
Divide 324 by the depth in inches. One yard covers 162 sq ft at 2 in, 108 sq ft at 3 in, and 81 sq ft at 4 in. You can use this to check a quote. For example, 32 yards spread 2 in deep should cover about 5,184 sq ft.
Should I buy bags or bulk?
Once you need about a cubic yard or more, the calculator suggests pricing bulk. One yard is 13.5 bags of 2 cu ft to carry. Bulk is priced by the cubic yard, and some suppliers set a delivery minimum, such as 3 yards. Ask for both the price per yard and the minimum before you decide.
How deep should mulch be?
University of Illinois Extension recommends 2 to 4 inches. Keep it at least 4 inches away from tree trunks and spread it out toward the dripline, not piled up in a cone. Deeper than 4 inches can starve roots of air.