Compost Calculator
How much compost to work into that garden bed?
How this is calculated
- Volume in cubic feet = length × width × (depth ÷ 12)
- Cubic yards = cubic feet ÷ 27, plus the settling allowance
- Bags = ⌈volume × 27 ÷ 2⌉ for standard 2 cu ft bags
Common questions
How much compost do I need for my garden bed?
A 10 × 10 bed topped with 2 inches of compost takes about 0.62 cubic yards — order 0.68 with the settling allowance, which is 10 of the 2 cu ft bags. For new beds, aim to work 2-3 inches into the top 6 inches of soil rather than layering it on top.
Can I add too much compost?
Yes — more is not better. Over about 25-30% organic matter by volume, you get excessive nutrient loads (phosphorus buildup especially), water retention problems, and plants that grow lush but weak. The 1-3 inch topdress worked into soil is the sweet spot; save the deep filling for raised beds with a balanced mix.
How many bags of compost are in a yard?
About 14 of the standard 2 cu ft bags per cubic yard. At $4-8 per bag that is $56-112/yd³ against $30-60 bulk delivered — above about 4 bags, bulk wins if you can take a delivery.
Compost vs topsoil — which do I need?
Compost is food (organic matter, microbes, nutrients); topsoil is structure (mineral soil for volume and drainage). New beds and low spots want topsoil (or a mix); existing beds with decent soil want compost. If plants were fine last year but lacked vigor — compost. If you are filling something — topsoil plus 10-20% compost.
Is homemade compost different from bought?
Mature homemade compost is excellent and free, but quality varies with what went in and whether it fully cooked (hot pile, turned, 130-160°F for weeks). Bought bulk compost from a reputable landscape supply is consistent and screened. Avoid unscreened "municipal" compost for beds — it can carry weed seeds and herbicide residue from treated lawn clippings.