Free Compost Estimator

♻️ FREE GARDEN TOOL

Compost Estimator

Work out how much compost you need to top-dress beds, improve soil or fill a bin — in cubic feet, cubic yards, wheelbarrows, bags and litres — plus the right green-to-brown mix.

✓ Free & instant   ✓ Imperial & metric   ✓ No sign-up needed

🧮 Compost Calculator

Please enter a length, width and depth greater than zero.

Your Results

Compost volume—
Cubic yards—
Bulk compost is sold by the cubic yard — 1 cubic yard = 27 cubic feet.
Wheelbarrows—
A standard wheelbarrow holds about 6 cubic feet when heaped.
Bags needed—
Your compost area preview will appear here

How to Estimate Compost

Use the volume formula: Length × Width × Depth = Volume. For top-dressing, 1–2 inches is plenty. For improving poor soil, dig in 2–3 inches. A new bed can take 3–4 inches mixed through the top 6–8 inches of soil.

Worked example: a 20 ft × 5 ft bed (100 sq ft) top-dressed at 2 inches: 100 × 2 ÷ 12 = 16.67 cubic feet, or 0.62 cubic yards. That is about 3 heaped wheelbarrows, or 12 bags of 1.5 cu ft compost, and about 472 litres.

JobCompost depthNotes
Annual top-dress, lawns0.5–1 in (1–3 cm)Spread thin, brush into grass
Top-dress, flower and veg beds1–2 in (3–5 cm)Keep it off plant stems
Improving poor soil2–3 in (5–8 cm)Dig or fork it in
New raised bed, compost layer3–4 in (8–10 cm)Mix with topsoil above

Common Mistakes to Avoid

  • Using unfinished compost — if it still smells or you can recognise the ingredients, let it cure longer. Unfinished compost can rob plants of nitrogen.
  • Spreading it too thick on lawns — more than an inch can smother grass. A thin, even layer is best.
  • Piling compost against stems and trunks — keep a few inches clear to prevent rot.
  • Forgetting the green-to-brown ratio — a compost pile needs roughly 1 part green (nitrogen-rich) to 3 parts brown (carbon-rich) by volume to heat up properly.
💡 Pro tip: Finished compost should be dark, crumbly and smell like forest soil. If your pile is slow, turn it, add water until it feels like a wrung-out sponge, and add more greens such as grass clippings or kitchen scraps.

Frequently Asked Questions

At 2 inches deep, a 10×10 ft bed (100 sq ft) needs 16.67 cubic feet — 0.62 cubic yards, or about 12 bags of 1.5 cu ft compost.
One cubic yard equals 27 cubic feet — about 18 bags of 1.5 cu ft, or 9 bags of 3 cu ft compost.
Yes. Very high rates can cause nutrient imbalances, especially phosphorus build-up. Stick to 1–3 inches per year for most beds, and test your soil every few years.
A hot, well-managed pile can finish in 2–3 months. A cold, unmanaged pile usually takes 6–12 months.
Homemade compost is usually richer in microbes and free, but its nutrient content varies. Bagged compost is consistent and weed-free, which is useful for seed sowing.

Related Garden Tools

Use it with the Raised Bed Soil Calculator, Mulch Calculator and Potting Soil Matrix. See all tools on the Free Tools page.