Enter the size of your garden bed and the depth you want to spread, and see how many cubic yards, cubic metres or bags of mulch to buy.
Cubic yards = (sq ft × depth in inches ÷ 12) ÷ 27
Shortcut: one cubic yard covers 324 sq ft at 1 in deep (108 sq ft at 3 in)
How to use the mulch calculator
Choose US or metric units and the shape of your bed — a rectangle, a circle (for example around a tree, entering the diameter as the length), or a known area if you already have it. Enter the depth you plan to spread, and optionally the bulk price per cubic yard or cubic metre and the price of a bag. The calculator shows how much mulch you need in bulk, how many bags that equals, and which option is cheaper. A table shows how the quantity changes at other depths.
The mulch formula
Cubic yards = (sq ft × depth in inches ÷ 12) ÷ 27
Shortcut: one cubic yard covers 324 sq ft at 1 in deep (108 sq ft at 3 in)
Depth is the part most people get wrong: it must be converted to the same unit as the area. Three inches is 0.25 ft; 7.5 cm is 0.075 m. In metric the maths is simpler — square metres × depth in metres gives cubic metres, and each cubic metre is 1,000 litres, the unit bagged mulch is sold in outside the US.
Worked example
A 20 × 10 ft border is 200 sq ft. Spread 3 inches deep, it needs 200 × 0.25 = 50 cubic feet, or 50 ÷ 27 = 1.85 cubic yards. Bagged mulch commonly comes in 2 cu ft bags, so you would need 25 bags — or 17 bags of the 3 cu ft size. At $40 per yard delivered in bulk the mulch costs about $74, versus $100 for 25 bags at $4. A metric bed of 6 × 3 m at 7.5 cm takes 1.35 m³, which is 1,350 litres or 27 bags of 50 L.
How deep should mulch be?
| Use | Recommended depth |
|---|---|
| Top-up of existing mulch | 1–2 in (2.5–5 cm) |
| Flower and shrub beds, fine shredded bark | 2–3 in (5–7.5 cm) |
| Coarse bark nuggets, wood chips, weed suppression | 3–4 in (7.5–10 cm) |
| Paths and play areas (wood chips) | 4–6 in (10–15 cm), more under play equipment |
More is not always better. Mulch deeper than about 4 inches can starve roots of oxygen and keep the soil too wet, and mulch piled against tree trunks ("volcano mulching") encourages rot and pests. Keep it a few inches away from stems and trunks, forming a doughnut rather than a cone.
Bulk or bagged?
Bulk mulch is usually far cheaper per cubic yard, but there is often a delivery fee and a minimum order, and a pile on the driveway needs moving quickly. As a rough rule, bags make sense for jobs under about 2 cubic yards (1.5 m³) or where you need to carry mulch through the house; bulk wins for larger projects. Bags are also easier to store and keep the colour of dyed mulch more consistent.
Choosing a mulch
- Shredded hardwood and bark knit together, stay put on slopes and break down to feed the soil.
- Pine bark nuggets last longer but can float away in heavy rain.
- Wood chips from tree surgeons are often free and excellent under trees and on paths.
- Compost and leaf mould improve soil quickly but need topping up more often.
- Stone and gravel do not decompose — see the gravel calculator, which converts volume to weight.
Quantities are estimates; fresh mulch settles by 10–20% over the first few weeks.
Cite or link to this page
Using this mulch calculator in an article, report or homework? Copy a citation or a ready-made link:
Calcivia. (2026). Mulch Calculator. Retrieved October 31, 2026, from https://www.calcivia.com/mulch-calculator/"Mulch Calculator." Calcivia, 2026, https://www.calcivia.com/mulch-calculator/. Accessed 31 Oct. 2026.<a href="https://www.calcivia.com/mulch-calculator/">Mulch Calculator</a> by Calcivia