Mulch Calculator & How Much Mulch You Need
Measures wood chips
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Work out how much mulch you need — from your bed area and spread depth get the volume in m³, the number of bags, the weight and trolley loads, and the cost.
Enter your area & material
Next: 7.5 cm is a solid layer — keep mulch a few cm clear of stems to avoid rot. Top up organic mulch as it breaks down.
Volume = area × depth; weight uses each material's bulk density. Order ~10% extra for settling.
Mulch — key facts
- Volume
- area × depth
- Typical depth
- 5–7.5 cm
- Straw
- ≈ 70 kg/m³
- Wood chips
- ≈ 280 kg/m³
- Gravel
- ≈ 1600 kg/m³
- Order extra
- ≈ 10% for settling
- 1 m³
- = 35.3 ft³ = 1.31 yd³
- Privacy
- Runs in your browser; nothing uploaded
Buy the right amount of mulch, once
Mulch is one of the highest-value jobs in the garden — it suppresses weeds, holds soil moisture, moderates temperature and (for organic types) feeds the soil as it breaks down. The only hard part is ordering the right quantity: too little and the beds are patchy, too much and you've wasted money and delivery. The maths is simple — volume = area × depth — but the weight and bag count depend on the material, which is where most guesses go wrong.
This calculator turns your bed size and chosen depth into the cubic metres, litres, bags, weight and trolley loads you need, using the real bulk density of each material from straw to gravel, plus an optional cost. Aim for a 5–7.5 cm layer, keep it clear of stems, order about 10% extra for settling, and top up organic mulch each year. Pair it with the Compost & Manure and Raised-Bed Soil tools to plan the rest of your beds.
Order accurately
Get the exact m³ and bags so you don't run short or over-buy.
Know the weight
See the tonnes and trolley loads — vital for heavy gravel or bark.
Pick the right depth
Use the recommended depth per material for weed control.
Budget the job
Add a price per bag to see the total mulch cost up front.
Frequently Asked Questions
How much mulch do I need?+
Multiply the area by the spread depth: volume (m³) = area (m²) × depth (m). For example, 50 m² at 7.5 cm needs 50 × 0.075 = 3.75 m³. This tool does it from your bed's length, width and depth and also gives the number of bags, the weight and the cost.
How deep should mulch be?+
About 5–7.5 cm (2–3 inches) for most organic mulches — deep enough to suppress weeds and hold moisture, but not so deep it suffocates roots. Fine materials like compost go thinner (≈5 cm); coarse wood chips and straw can go to 7.5 cm. The tool shows the recommended depth for each material.
How many bags of mulch is that?+
It depends on the bag size. Bagged mulch is usually sold in litres (e.g. 50 L) or cubic feet. The tool divides your total volume by the bag size to give the bag count, and tells you roughly how many square metres one bag covers at your chosen depth.
How much does mulch weigh?+
It varies a lot by material — straw is very light (~70 kg/m³), wood chips and bark are moderate (~250–280 kg/m³), compost is heavier (~450 kg/m³) and gravel is very heavy (~1600 kg/m³). The tool uses each material's bulk density to estimate the total weight and trolley loads.
Should I order extra mulch?+
Yes — order about 10% extra. Loose material settles and compresses, beds are rarely perfectly even, and you'll want a little spare to top up thin spots. It's cheaper to have a small surplus than to run short and re-order delivery.
Which mulch is best?+
It depends on the use: wood chips and bark last longest around trees and shrubs; straw and dry leaves are cheap and great for vegetable beds; compost feeds the soil as it breaks down; gravel suits paths and drought planting. Organic mulches improve soil but need topping up yearly.
Does mulch stop weeds?+
A 5–7.5 cm layer blocks light and greatly reduces weed germination. For heavy weed pressure, lay cardboard or a weed mat under the mulch. Keep the layer topped up, because as organic mulch thins and breaks down weeds find the gaps.
Can mulch harm my plants?+
Only if misused. Piling mulch against stems and trunks ("mulch volcanoes") traps moisture and causes rot — keep it a few centimetres clear of stems. Very thick fresh wood chips can temporarily tie up nitrogen at the surface; keep them as a top layer, not dug in.
How do I convert to cubic feet or yards?+
1 m³ = 35.3 cubic feet = 1.31 cubic yards. The tool reports cubic metres and litres; multiply m³ by 35.3 for cubic feet or by 1.31 for cubic yards if your supplier sells by those units.
Does the calculator handle gravel and stone?+
Yes — select gravel/stone as the material and it uses a stone bulk density (~1600 kg/m³), so the weight and number of bags reflect how heavy stone is. Use a shallower depth (≈5 cm) for decorative stone over a weed membrane.
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