Compost Calculator
Compost improves soil structure, water holding and biological life, but the right amount depends on how you use it. A lawn needs only a thin dusting, while a new vegetable bed might get several inches worked in. Choose an application or enter your own depth to see the volume and bag count.
How to use this calculator
- Choose units and enter the size of the area.
- Pick an application preset, or type a custom depth.
- Read the result in cubic feet, cubic yards and liters, plus bag counts.
- If mixing in, spread the compost evenly first, then fork or till it into the top 6–8 inches of soil.
Typical compost rates
Lawns: top-dress with about ¼ to ½ inch, raked into the grass so the blades still show. Established beds: about 1 inch spread on the surface each year is a common maintenance rate. New beds or poor soil: 2 to 3 inches mixed into the top 6–8 inches. Going much higher is rarely needed and, with manure-based composts, can add more nutrients (especially phosphorus) than plants use.
Converting to bags
Bagged compost in the US is often sold in 0.75, 1 or 1.5 cu ft bags; in metric countries 40 or 50 liter bags are common. The calculator shows both. For more than about a cubic yard, bulk compost from a municipal or landscape supplier is usually far cheaper.
Homemade compost
If you make your own, a typical home bin of 3 × 3 × 3 ft holds 1 cubic yard of raw material, which shrinks substantially as it breaks down – often yielding well under half that volume of finished compost.
Frequently asked questions
How much compost do I need per square foot?
At 1 inch deep you need 1/12 cu ft per square foot, so 100 sq ft needs about 8.3 cu ft. At 2 inches, double that.
How much compost for a 4×8 raised bed?
A 1 inch top-up on 32 sq ft is about 2.7 cu ft – roughly two 1.5 cu ft bags. Mixing in 2 inches takes about 5.3 cu ft.
Can I add too much compost?
Yes. Very heavy, repeated applications – especially of manure compost – can build up excess nutrients and salts. Moderate yearly additions are usually best.
How thick should compost be on a lawn?
About ¼ to ½ inch, raked in so it settles between grass blades. Thicker layers can smother the grass.