How Much Mulch Do You Need?
By the TapeMeasureCalc team · Updated · 6 min read
Buying mulch by guesswork usually means a second trip to the garden centre or a pile left over. Three numbers decide the quantity: the area of your beds, the depth you want, and the size of the bags or the unit of bulk delivery.
Choose a mulch depth
Gardening references commonly suggest a layer of around 2–3 inches (50–75 mm) for most beds, with up to about 4 inches (100 mm) for coarse materials or weed suppression on bare ground. Thicker layers are not always better: very deep mulch can keep soil waterlogged and reduce air reaching roots.
- Topping up existing mulch: measure what is left and add only the difference.
- Fine materials such as compost are usually applied more thinly than chunky bark.
- Keep mulch clear of tree trunks and plant stems.
Measure your beds
For rectangular beds, multiply length by width. For other shapes:
- Circle: 3.1416 × radius². A round bed 8 ft across has a 4 ft radius: 3.1416 × 16 = 50.3 sq ft.
- Triangle or corner bed: ½ × base × height.
- Curved border: measure the length along the middle of the bed and the average width.
- Ring around a tree: area of the outer circle minus the trunk area (often small enough to ignore).
Turn area and depth into volume
Volume (ft³) = Area (sq ft) × Depth (in) ÷ 12
Cubic yards = Cubic feet ÷ 27
Example: 300 sq ft of beds at 3 inches needs 300 × 3 ÷ 12 = 75 ft³, which is 75 ÷ 27 = 2.78 cubic yards.
In metric there is a handy shortcut: the depth in millimetres equals litres per square metre. 75 mm over 20 m² is 75 × 20 = 1,500 litres, or 1.5 m³.
Quick coverage table
| Depth | 1 cubic yard covers | One 2 ft³ bag covers |
|---|---|---|
| 2 in | 162 sq ft | 12 sq ft |
| 3 in | 108 sq ft | 8 sq ft |
| 4 in | 81 sq ft | 6 sq ft |
Bags or bulk?
Bags are convenient for small areas and easy to carry, and they store neatly. Bulk mulch, delivered by the cubic yard or cubic metre, often costs less per unit for larger jobs, but there may be a delivery charge and you need somewhere to tip it.
To compare, convert both to the same unit. One cubic yard equals 13.5 bags of 2 ft³. If bags cost 4 each, a cubic yard of bagged mulch costs 14 × 4 = 56 (rounding up to whole bags), which you can set against a bulk price plus delivery.
Allow for settling
Fresh mulch is fluffy and settles after rain and watering. Bags may also be filled loose. Many gardeners buy slightly more than the calculated figure, especially for light materials like pine straw or shredded leaves. It is easier to spread a little extra than to make another trip.
Use the calculator
The mulch calculator adds up several beds, offers 2, 3 and 4 inch presets (or 50, 75 and 100 mm), and gives bag counts and bulk cost side by side. Filling new raised beds? Use the raised bed soil calculator. For any other volume, the cubic yard calculator converts dimensions directly.