Mulch Guide: Everything You Need to Estimate
To calculate mulch, multiply the bed length by width to get the area, then by depth in feet, and divide by 27 for cubic yards. A 20×4 ft bed at 3 inches deep needs about 0.74 cubic yards (roughly 10 bags), costing about $22–$37 in bulk mulch.
Get exact numbers
Use the free Mulch Calculator to estimate your project.
How to estimate mulch
Formula: Mulch (yd³) = (Length ft × Width ft × Depth ft) ÷ 27
- Measure the bed. Record length and width in feet.
- Choose a depth. Convert inches to feet (3 in = 0.25 ft).
- Find the volume. Multiply area × depth for cubic feet.
- Convert to yards. Divide cubic feet by 27, or by 13.5 for 2 ft³ bags.
Example: A 20 ft × 4 ft bed at 3 in deep: 80 ft² × 0.25 ft = 20 ft³ ÷ 27 ≈ 0.74 yd³ (≈ 10 bags).
Common mistakes to avoid
Mulching too deep
More than 3–4 inches suffocates roots and holds excess moisture. Two to three inches is the sweet spot.
Piling mulch against stems
"Mulch volcanoes" around trunks invite rot and pests. Keep mulch a few inches clear of stems and trunks.
Ignoring existing mulch
If a bed already has mulch, you usually only need a 1-inch refresh — measure for the top-up, not the full depth.
Buying bags for big beds
For large areas, bulk mulch by the cubic yard is far cheaper than bagged. Compare price per cubic foot.