How to use the mulch calculator
- Choose the bed shape — rectangle, circle (tree rings) or enter the area directly.
- Enter the measurements and the depth of mulch you want.
- Pick the bag size you plan to buy. In the US most bags are 2 or 3 cu ft; in the UK and Europe 50–75 L.
- Optional: enter a bag price and a bulk price per cubic yard (or m³) to compare.
For irregular beds, break them into rectangles and circles, work each out, and add the areas together in “I know the area”.
Mulch formula
Volume (ft³) = Area (ft²) × Depth (in) ÷ 12 Cubic yards = Cubic feet ÷ 27 Bags = Cubic feet ÷ Bag size (cu ft) → round up
Worked example
A 20 × 10 ft flower bed, 3 inches deep:
- Area = 200 ft²; depth = 3 ÷ 12 = 0.25 ft
- Volume = 200 × 0.25 = 50 ft³ = 1.85 cubic yards
- 2 cu ft bags: 50 ÷ 2 = 25 bags
Mulch coverage chart
| Depth | 1 cubic yard covers | One 2 cu ft bag covers | 1 m³ covers |
|---|---|---|---|
| 1 in (2.5 cm) | 324 ft² | 24 ft² | 40 m² |
| 2 in (5 cm) | 162 ft² | 12 ft² | 20 m² |
| 3 in (7.5 cm) | 108 ft² | 8 ft² | 13.3 m² |
| 4 in (10 cm) | 81 ft² | 6 ft² | 10 m² |
Choosing and laying mulch
- Shredded hardwood knits together and stays put on slopes. Bark nuggets last longer but can wash away. Pine straw is light and good for acid-loving plants.
- Weed first. Pull weeds and water the soil before mulching; a layer of cardboard underneath helps smother tough weeds.
- Avoid “volcano” mulching around trees — keep a gap of 3–6 in (7–15 cm) around the trunk.
- Top up yearly. Organic mulch breaks down by about an inch a year, which feeds the soil.
- Bulk mulch settles a little after spreading; ordering 5–10% extra gives a full-looking bed.
Measuring irregular beds and tree rings
Most garden beds are not perfect rectangles. A quick way to measure a curved bed is to take its longest length and its average width (measure the width in three or four places and average them), then multiply. For a kidney or oval bed this is usually within 10% of the true area. For a ring of mulch around a tree, measure the full diameter of the ring and use the Circle option — the small area of the trunk makes almost no difference. Paths and play areas use the same method, but wood chips for playgrounds are normally laid much deeper, around 9–12 inches (23–30 cm), to cushion falls, so enter that depth instead.