Depth to bags
Measure the area actually being covered.
- Volume = area × depth. Keep mulch clear of stems and use a depth suitable for the chosen material and plants.
Garden calculator
Mulch Calculator
Calculate mulch or bark from area and depth, or use a supplier’s stated litres-per-area rate.
What does a worked calculation look like?
A 5 × 4 m bed mulched 7 cm deep needs 1.4 m³. With a 10% allowance that is 1,540 L, or 31 bags of 50 L.
Method and practical checks
- Volume = area × depth. Keep mulch clear of stems and use a depth suitable for the chosen material and plants.
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Every calculation option
Bark coverage rate
Use this mode when the supplier quotes litres per square metre.
- The supplier’s coverage rate assumes a particular depth. Do not add that depth a second time.
Worked example
A 5 × 4 m bed mulched 7 cm deep needs 1.4 m³. With a 10% allowance that is 1,540 L, or 31 bags of 50 L.
| Input | Value |
|---|---|
| Measured sections | Length 5 m, Width 4 m |
| Mulch depth | 7 cm |
| Extra allowance | 10 % |
| Pack size | 50 L |
| Result | Value |
|---|---|
| Volume before allowance | 1.4 m³ |
| Required quantity | 1,540 L |
| Packs to buy | 31 |
| Purchase quantity | 1,550 L |
| Left over | 10 L |
Reading the result
- The RHS recommends organic mulch at least 5 cm and ideally 7.5 cm thick for weed suppression and moisture retention.
- Keep mulch away from the stems of woody plants.
- If the supplier states a coverage rate in litres per square metre, use the rate mode and do not also enter a depth.
Sources and further reading
- RHS: mulches and mulching — Organic mulch at least 5 cm and ideally 7.5 cm thick, kept off woody stems.
Why does the mulch depth change the order so much?
Volume is area multiplied by depth. Doubling the depth doubles the volume before pack rounding. Convert centimetres to metres when working by hand: 20 m² at 5 cm needs 1 m³, or 1,000 L. Choose a depth suitable for the material and planting.
Can I calculate mulch from its bag weight?
Use the stated bag volume if available. Wood chips, bark and other mulches can have very different density and moisture content. The tool's pack rounding uses volume, so a kilogram label alone cannot establish how many litres the bag will cover.
How should I measure an irregular mulching area?
Split the area into shapes you can measure, calculate their areas and add them before applying the chosen depth. Leave out paths and other spaces you will not cover. Convert centimetres of depth to metres for a cubic-metre result, then compare that volume with the supplier's actual bag or bulk quantity.
Calculation/content reviewed 4 October 2026. Source: Babushka Market’s displayed formulas, units and labelled editable assumptions. How the estimates work