Compost Calculator — Cubic Yards & Bags
Estimate how much compost you need in cubic yards and bags from the area and the depth you want to spread.
Calculator
Top-dressing 400 sq ft at 2.0 in needs about 2.47 cu yd of compost — roughly 34 bags. A 1/4–1/2 in top-dress is common for lawns; beds take more. Confirm the bag coverage.
Compost is the cheapest upgrade a yard can get: worked into beds it feeds the soil, and top-dressed over a lawn it improves structure without smothering the grass. Because compost is spread as a layer, the amount you need is area×depth converted to cubic yards, and this tool also tells you how many bags that is so you can compare against a bulk load.
Building a new bed? Pair this with the topsoil calculator for the base soil, then the mulch calculator for the finishing layer on top.
Formula
Compost volume follows the same slab geometry, and bags come from cubic feet:
cubic yards = area (sq ft) × depth (in) ÷ 324
bags = ceil( cubic yards × 27 ÷ bag size in cu ft )
The 324 constant is 27 cu ft per cubic yard times 12 in per foot. Bagged compost is usually 1 or 2 cu ft, so a cubic yard is 13.5 bags of 2 cu ft or 27 bags of 1 cu ft — set the bag size to match what you buy.
Worked example
To top-dress 400 sq ft with a 2 in layer using 2 cu ft bags:
- Volume:
400 × 2 ÷ 324 = 2.47 cu yd - Bags:
2.47 × 27 ÷ 2 = 33.3, rounded up to 34 bags
So the job is about 2.47 cubic yards of compost, roughly 34 bags.
Spreading compost the right way
Compost tips:
- Top-dress a lawn thinly. Over grass, a 1/4 to 1/2 in layer is plenty — deeper and you smother the turf. Beds can take 1–3 in worked into the soil.
- Let it finish. Use fully finished, dark, crumbly compost. Unfinished compost robs nitrogen from the soil as it keeps breaking down.
- Bulk for big jobs. Above a couple of cubic yards, bulk compost by the yard beats bags on price — compare with the bulk-material cost calculator.
- Confirm the bag size. Compost bags range from 0.75 to 2 cu ft; check the label and set the bag size so the count is right.
Reference table
Cubic yards of material by area and depth (cu yd = area × depth ÷ 324). Bulk materials are usually sold by the cubic yard or ton, so round up and buy about 5–10% extra.
| Depth | 100 sq ft | 300 sq ft | 500 sq ft | 1,000 sq ft |
|---|---|---|---|---|
| 1 in | 0.31 cu yd | 0.93 cu yd | 1.54 cu yd | 3.09 cu yd |
| 2 in | 0.62 cu yd | 1.85 cu yd | 3.09 cu yd | 6.17 cu yd |
| 3 in | 0.93 cu yd | 2.78 cu yd | 4.63 cu yd | 9.26 cu yd |
| 4 in | 1.23 cu yd | 3.70 cu yd | 6.17 cu yd | 12.35 cu yd |
| 6 in | 1.85 cu yd | 5.56 cu yd | 9.26 cu yd | 18.52 cu yd |
See the full breakdown, including bags per cubic yard, on the material-coverage table.
Frequently asked questions
How much compost do I need?
400 × 2 ÷ 324 = 2.47 cubic yards, about 34 bags of 2 cu ft.