Compost Calculator
Estimate how much compost you need by volume, bags, weight, and cost for one or many garden beds — rectangular or circular. Imperial or metric.
Beds
Bed preview (to scale, top-down)
1 unit = 0.06 ftTypical: 5% for top-dressing, 10% if you're mixing into existing soil, 15% for fluffy compost that will settle.
Tick "Include" to estimate bag count or bulk delivery cost.
Your estimate
About Compost Calculator
The Compost Calculator works out how much compost to buy for any garden bed, raised bed, border, or planter — in cubic feet, cubic yards, cubic metres, bags, or delivery yards. It also estimates the approximate weight so you can plan whether to carry bags home or order a bulk drop.
Add as many beds as you like and pick a shape for each (rectangular or circular). A small to-scale top-down preview keeps your garden layout visible while you type, and a waste slider lets you allow for settling and the extra you'll want when mixing compost into existing soil.
How to Use Compost Calculator
- 1 Pick your unit. Imperial (feet + inches) or Metric (metres + centimetres) — length and width use the bigger unit, depth uses the smaller one.
- 2 Add each bed. For rectangular beds enter length and width; for round planters or circular beds enter the diameter. Click "Add another bed" for as many shapes as you need.
- 3 Set the depth. The compost layer's thickness. 1–2" is typical for top-dressing or mulching, 2–4" for amending soil, 4–6"+ for filling a new raised bed.
- 4 Adjust waste / settling. 5% covers minor settling for top-dressing. Bump it up if you're digging compost into existing soil or it arrives very light and fluffy.
- 5 (Optional) Cost it. Tick "Include" and switch between Bags (pick bag size and price per bag) or Bulk delivery (price per cubic yard or per cubic metre). The estimate panel shows total cost.
- 6 Check weight. Compost is lighter than topsoil, but a cubic yard still weighs roughly half a ton — the weight column helps you decide between carrying bags and getting a delivery.
Frequently Asked Questions
How deep should I spread compost? ▾
Depends on the job:
- Top-dressing a lawn: 0.25–0.5" (6–12mm)
- Mulching around plants: 1–2" (2.5–5cm)
- Amending / digging into beds: 2–4" (5–10cm)
- Filling a new raised bed (with soil): 4–6" (10–15cm) of compost
- No-dig bed top layer: 2–3" (5–8cm) fresh each season
How much does a cubic yard of compost weigh? ▾
Around 1,000–1,100 lbs (450–500 kg) for a cubic yard of moist compost — about half the weight of topsoil. A cubic metre is roughly 600–700 kg. This calculator uses ~40 lbs/ft³ (650 kg/m³) as a damp average. Bagged, screened compost is often lighter; very wet or manure-based compost is heavier.
Bags or bulk delivery — which is cheaper? ▾
Bagged compost usually costs 2–4× more per cubic yard than bulk. Bulk delivery wins above roughly ½ cubic yard (≈ 13 ft³, ≈ 7 bags of 2 ft³) — as long as you have somewhere a tipper can drop it. Bags are easier for small jobs, tight access, balconies, or when you only need a few.
What's the difference between compost and topsoil? ▾
Compost is fully decomposed organic matter — rich in nutrients but light and not a structural soil on its own. Topsoil contains mineral particles and gives a bed its body. For new beds, fill the bulk with topsoil and finish with a compost layer, or mix roughly 50/50. For established beds, just top-dress with 1–2" of compost each season. Use this calculator for either — pick the right depth.
Can I use too much compost? ▾
Yes. A layer thicker than about 3–4" used on its own can hold too much water, run high in nutrients (especially phosphorus), and starve roots of oxygen. For most beds, 1–3" worked into or laid over existing soil is plenty. Build deep beds with a soil-plus-compost blend rather than pure compost.
How do I convert bags to cubic yards or metres? ▾
There are 27 cubic feet in a cubic yard, so a cubic yard is about 14 bags of 2 ft³ (or 27 of the 1 ft³ size). In metric, 1 cubic metre = 1,000 litres, so a 50 L bag is 0.05 m³ and you need 20 bags per cubic metre. This calculator does the maths for you once you choose a bag size.
Is my data saved or sent anywhere? ▾
No. Everything runs in your browser. Your bed dimensions and prices never leave your device and nothing is stored on a server.