How mulch is calculated
Volume (ft³) = length × width × (depth in inches ÷ 12)
Cubic yards = ft³ ÷ 27
Bags = ft³ ÷ cubic feet per bag, rounded upWorked example: a 20 × 10 ft bed, 3 in deep
- Volume: 20 × 10 × (3 ÷ 12) = 50 ft³.
- In cubic yards: 50 ÷ 27 = 1.85 yd³.
- In 2 cu ft bags: 50 ÷ 2 = 25 bags.
How deep should mulch be?
| Situation | Typical depth |
|---|---|
| Fine or shredded mulch around plants | 2–3 in |
| Coarse bark or wood chips | 3–4 in |
| Topping up last year's mulch | 1–2 in, up to a total of 3–4 in |
Measure what's already there before topping up, as old mulch may still be thick enough. Keep mulch a few inches away from tree trunks and plant stems. Piling it against them can trap moisture and invite rot.
Bags or bulk?
One cubic yard equals 27 ft³, which is 13.5 bags of the common 2 cu ft size. The example bed would take 25 bags, or just under 2 yd³ in bulk. Bulk mulch is often cheaper per yard for larger jobs, but delivery fees, minimum orders and a place to dump the pile can change the math. Bags are often simpler for small beds, and they're easier to move across a yard. Compare local prices for your exact quantity.
Measuring irregular beds
- Curved beds: average the width at several points, then multiply by the length.
- Circles around trees: a circle covers about 21% less than the square around it, so entering its diameter as both length and width leaves you with some extra.
- Several beds: add each one to your buy list, or add their areas together when buying in bulk.
Improving the soil first? The topsoil calculator works the same way, and allows for settling.