About the compost calculator
Compost improves soil structure, helps sandy soil hold water, and loosens heavy clay. How much you need depends on how you're using it: a thin top-dressing over a lawn takes far less than working a thick layer into a new vegetable bed.
Enter the size of the area and the depth of compost you plan to spread on the surface. The calculator converts it to volume and bags.
How to use this calculator
- Measure the length and width of the bed or lawn area.
- Choose a depth: the layer of compost you'll spread before mixing it in, not the depth you'll dig to.
- Pick your bag size and an allowance, then review the results.
Worked examples
- Spread 2 in of compost over 100 sq ft.
- 100 × 2 ÷ 12 = 16.7 cu ft
- 16.7 ÷ 27 = 0.62 cu yd
17 bags of 1 cu ft before any allowance.
- Spread ¼ in (0.25 in) over 2,000 sq ft.
- 2,000 × 0.25 ÷ 12 = 41.7 cu ft
- 41.7 ÷ 27 = 1.54 cu yd
About 1.5 cu yd — usually more practical to buy in bulk.
Measurement guidance
Typical compost depths
New garden beds: 2–3 inches worked into the top 6–8 inches of soil. Yearly bed maintenance: about 1 inch. Lawn top-dressing: ¼ to ½ inch, raked in so grass blades still show.
Mixing ratios
If you're blending compost into soil for a bed, a mix of roughly one part compost to two or three parts soil is a common starting point. Use the Raised Garden Bed Calculator for the total, then split it by ratio.
Frequently asked questions
How much compost should I add to a garden bed?
For a new bed, 2–3 inches spread over the surface and mixed in is common. For an established bed, about an inch each year is usually enough.
Can I put compost directly on my lawn?
Yes, in a thin layer. Spread ¼–½ inch and rake it in so it settles between the grass blades. Thicker layers can smother the lawn.
Is compost the same as soil?
No. Compost is decomposed organic matter used to improve soil. Most plants grow best in soil that has compost mixed in rather than in pure compost.