Mulch Calculator
Getting Mulch Depth Right, Not Just Coverage
Mulch is sold by the cubic yard or the bag, but gardeners think in square feet of bed space. The conversion between the two hinges entirely on depth, and depth is where most over-ordering and under-ordering happens — a bed mulched at 4 inches instead of the recommended 2–3 inches burns through a third more material than necessary, while too thin a layer fails to suppress weeds or hold soil moisture. This calculator converts a bed's area and target depth directly into cubic yards and bag count, so you order the right amount the first time.
The Formula
Volume (cu yd) = Volume (cu ft) ÷ 27
Bags Needed = ceiling(Volume (cu ft) ÷ Bag Size)
Depth is entered in inches and divided by 12 to convert to feet before multiplying by area, since area is measured in square feet. The result in cubic feet is then divided by 27 (the number of cubic feet in a cubic yard) for the bulk-order figure, or divided by bag size and rounded up for a bagged-goods order.
Where This Matters
- New bed installation — ordering bulk mulch by the cubic yard from a landscape supplier requires knowing the total volume in advance, since delivery minimums and per-yard pricing make guessing expensive.
- Annual top-dressing — established beds typically need a thinner refresh layer (1–2 inches) rather than a full 3-inch application, and the same formula scales down cleanly.
- Bag vs. bulk decisions — bagged mulch is convenient for small beds but costs considerably more per cubic yard than bulk delivery; knowing the exact volume tells you which crossover point applies to your project.
| Bed area | 2 in depth | 3 in depth | 4 in depth |
|---|---|---|---|
| 100 sq ft | 0.62 cu yd | 0.93 cu yd | 1.23 cu yd |
| 200 sq ft | 1.23 cu yd | 1.85 cu yd | 2.47 cu yd |
| 500 sq ft | 3.09 cu yd | 4.63 cu yd | 6.17 cu yd |
| 1,000 sq ft | 6.17 cu yd | 9.26 cu yd | 12.35 cu yd |
At a standard 3-inch depth with 2 cu ft bags, a 100 sq ft bed needs 13 bags; a 1,000 sq ft bed needs 125 bags — the point at which bulk delivery is almost always cheaper.
How to Use This Calculator
- Enter the bed area in square feet.
- Enter the target depth in inches (defaults to 3 in, the standard recommendation for garden beds).
- Enter the bag size in cubic feet if you're buying bagged mulch (defaults to 2 cu ft, a common bag size).
- Select Calculate for the total volume in cubic yards and the number of bags needed.
Related Calculations
For a similar bulk-material conversion, see the Topsoil Calculator, or check Gravel Calculator for hardscape base material by weight.