How to calculate how much mulch or gravel you need
Mulch, gravel, and soil are all sold by volume, so the math is length times width times depth. The only conversion is depth: it's chosen in inches but has to become feet before multiplying, then the result is divided down to cubic yards, which is how bulk material is ordered.
cubic feet = length(ft) × width(ft) × (depth(in) ÷ 12)
cubic yards = cubic feet ÷ 27
bags = round up(cubic feet ÷ bag size)
Worked example
A 20 ft × 10 ft bed at 3 inches deep is 200 × 0.25 = 50 cubic feet, or about 1.85 cubic yards. In standard 2-cubic-foot bags that's 25 bags — which is exactly where most people switch to a bulk delivery instead.
How deep should mulch or gravel be?
Depth drives everything, so start here. These are the common depths by purpose:
| Use | Recommended depth |
|---|
| Refreshing existing mulch | 1–2 inches |
| New mulch bed (weed control) | 3–4 inches |
| Gravel walkway | 2–3 inches |
| Gravel driveway base | 4–6 inches |
One cubic yard of mulch covers about 100 square feet at 3 inches deep, or 160 square feet at 2 inches. A standard 2-cubic-foot bag covers roughly 8 square feet at 3 inches.
Frequently asked questions
How many bags of mulch are in a cubic yard?
There are 13.5 bags of 2-cubic-foot mulch in a cubic yard, since a cubic yard is 27 cubic feet. For 3-cubic-foot bags it's 9 bags per yard.
How much does a yard of mulch cover?
One cubic yard covers about 100 square feet at 3 inches deep, 160 square feet at 2 inches, or 80 square feet at a deep 4-inch layer.
Is it cheaper to buy mulch in bags or in bulk?
Bags are convenient for small beds, but bulk mulch by the cubic yard is usually much cheaper once you need more than about one yard — roughly 14 or more standard bags.
How much does mulch cost?
Bagged mulch is often $3 to $5 per 2-cubic-foot bag. Bulk mulch typically runs $30 to $50 per cubic yard, plus a delivery fee, which is why bulk wins on larger jobs.