How it works
Planning a garden bed refresh means figuring out how much mulch to buy. Enter the length and width of your planting area, the desired mulch depth, and the bag size available at your local home improvement store. The calculator returns the total mulch volume in cubic yards and the number of bags to pick up.
Landscaping suppliers and nursery yards sell bulk mulch by the cubic yard, while hardware stores carry bagged mulch in 1.5 or 2 cubic foot options. This tool handles both purchasing paths so you can compare costs. A key distinction: mulch depth follows horticultural guidelines for weed suppression and moisture retention — it has nothing to do with the structural thickness requirements that govern poured concrete slabs.
The formula
Cubic Yards = (Length (ft) × Width (ft) × Depth (in)) / 324
The 324 divisor converts inches to feet (÷12), then cubic feet to cubic yards (÷27).
Worked example
Say you have a 200 sq ft garden bed and want a 3-inch mulch layer. The bed measures 20 ft by 10 ft, giving 200 square feet of coverage area.
Cubic yards: (20 × 10 × 3) / 324 = 600 / 324 = 1.85 cu yd
Cubic feet: 1.85 × 27 = 49.95 ≈ 50 cu ft
For bagged mulch in 2 cu ft bags:
Bags needed: 50 / 2 = 25 bags
For 1.5 cu ft bags instead:
Bags needed: 50 / 1.5 = 33.3 → 34 bags
Round up to the nearest whole bag — you cannot buy a partial bag at the register.
Tips
| Mulch depth | Best use case |
|---|---|
| 1–2 in | Annual top-up over existing mulch |
| 2–3 in | Standard flower beds and shrubs |
| 3–4 in | New beds or aggressive weed control |
Add 5–10% extra for settling and uneven ground. Avoid piling mulch against tree trunks — leave a small gap to prevent rot. A 3-inch layer is a solid middle ground for fresh beds, while established planting areas often need only a 1-inch refresh each season.
This calculator provides an estimate for planning your nursery run, not a professional landscaping quote.