Compost Calculator
Estimate how much compost to buy for top-dressing, soil amendment, or raised-bed top-ups, in cubic feet, cubic yards, and bag count, with bagged-vs-bulk cost guidance.
Part of your self-sufficiency setup. For filling a new raised bed from scratch (8–12 in deep), use the Raised Bed Soil Calculator instead.
Calculate compost needed
Enter the area dimensions, compost layer depth (1–3 inches is typical), and the bag size you'll buy. Results, bag count, and a bagged-vs-bulk recommendation appear instantly.
33.33 ft³
Based on a 20 ft by 10 ft area with a compost layer of 2 inches.
How to use this calculator
Enter the area length and width in feet, then enter how deep you want to apply compost. The calculator estimates cubic feet, cubic yards, and optional bag count.
Tips for success
- Compost is often spread in a 1 to 3 inch layer depending on the purpose.
- Top dressing and soil amendment need less material than full bed filling.
- Bagged compost is handy for small areas, but bulk delivery may be cheaper for larger beds.
- Compost improves soil structure, fertility, and moisture retention.
- Many vegetable gardens benefit from regular compost additions.
Practical note
This tool is useful for home gardeners, raised bed growers, and anyone improving soil for food production and self-sufficiency.
Common mistakes
- Going too deep. Compost is an amendment, not a fill. 1–3 inches is the standard application range; deeper than that and you're filling the bed, which calls for raised-bed mix or topsoil instead.
- Confusing application depth with bed depth. A 12 inch raised bed doesn't need 12 inches of compost. Compost goes on top of (or mixed into the top few inches of) existing soil.
- Trusting bag labels without checking. Compost bags range from 0.75 to 2 ft³, and the printed cubic-foot value matters more than the brand. Match what's on the bag to what you enter here.
- Measuring irregular areas as rectangles. Curved beds and L-shapes need to be broken into smaller rectangles, calculated separately, and added together.
- Not rounding up. Add 10% to your calculated volume so you have enough to top off uneven spots and the edges of the bed.
FAQ
How much compost should I add to a garden bed?
Many gardeners use about 1 to 3 inches depending on whether they are top dressing or heavily amending soil.
Can I use this for raised beds?
Yes. It works well for compost additions to raised beds and garden boxes.
How many cubic feet are in one cubic yard?
One cubic yard equals 27 cubic feet.
Should I buy extra compost?
Usually yes. A little extra helps cover uneven areas and small measuring errors.