Compost Calculator: How Much Compost Do I Need?
Compost is the backbone of healthy soil, whether it is spread on top every year, used to build no-dig beds or dug into a new border. Each job uses a very different depth.
Runs in your browser. Nothing you enter is stored.
What this calculator does
Pick your job and enter the area. The calculator works out the compost volume, the bags or bulk to order and an approximate weight for transport.
How to use the compost calculator
- Enter the length and width of the area and how many similar areas you have.
- Pick a job to load a typical depth, or enter your own.
- Enter the bag size you can buy.
- Compare the bag count with the bulk volume.
- Spread compost when the soil is moist; no need to dig it in on established beds.
How the calculation works
area = length × width × areas volume = area × depth bags = ceil(volume ÷ bag size) weight ≈ volume × 0.6 t/m³
Finished compost typically weighs around 500–700 kg per cubic metre; the calculator uses 600 kg as a guide for transport.
Worked example
Top-dressing 20 m² of beds with 5 cm of compost takes 1 m³: 20 bags of 50 L, weighing roughly 600 kg.
Assumptions and limitations
- Weights vary with moisture; wet compost can be much heavier.
- Home-made compost is often lumpier and less dense than bagged compost.
- No-dig beds need a deep first layer, then about 2.5 cm (1 in) a year.
Frequently asked questions
How much compost should I add to my garden each year?
About 2.5–5 cm (1–2 in) spread on top each year is a common, generous amount for vegetable beds.
How much area does a cubic yard of compost cover?
About 324 square feet at 1 inch deep, or 162 square feet at 2 inches.
Can you put too much compost on a garden?
Very heavy, repeated applications can build up excess nutrients such as phosphorus. Moderate yearly top-ups are best.
How do I top-dress a lawn with compost?
Spread a thin layer of fine compost, about 6 mm (1/4 in), and brush it into the grass after aerating.
What is the best C:N ratio for compost?
About 25–30 parts carbon to 1 part nitrogen. Use the compost C:N ratio calculator to balance greens and browns.