Compost Calculator

Tell us your bed size and how deep you want it, and we'll figure out exactly how much compost to buy.

📖 How it works & FAQ

Bed length (ft)

Bed width (ft)

Depth (inches)

Bag size (cu ft)

0Cubic feettotal compost volume

0Cubic yardsif buying in bulk

0Bags to buyat 1.5 cu ft each

How much compost do you need?

Working out compost by guesswork usually means an extra trip to the garden center or a pile of leftover bags. The math is simple once you break it down: compost is sold by volume, so you just need the area of your bed multiplied by how deep you want the layer. This calculator does that instantly and converts the result into cubic feet, cubic yards, and the number of bags to grab.

The volume math

Volume equals length times width times depth. Because depth is measured in inches but length and width are in feet, we divide the depth by 12 to keep the units matched. That gives cubic feet. Divide cubic feet by 27 for cubic yards (handy when a supplier sells compost in bulk by the yard), and divide by your bag size to see how many bags to buy. We always round bags up, since you can't buy a partial bag. It's the same volume formula used for mulch or topsoil.

How to use it

Measure your bed's length and width in feet.
Decide your depth in inches. A 1–2 inch top-dressing refreshes existing beds; 3–4 inches is common for building a new bed.
Enter the bag size printed on the compost you plan to buy (1.5 cu ft is typical).
Read your cubic feet, cubic yards, and bag count instantly — no button to press.

These figures are planning estimates, not professional landscaping advice — buy a little extra to allow for settling and uneven ground.

FAQ

How deep should compost be?: For topping up established beds, 1–2 inches works well. For starting a new bed or heavily amending soil, aim for 3–4 inches and mix it in.
My bed isn't a rectangle — what do I do?: Break it into rectangles, calculate each, and add them up. For circles, use roughly length × width of the widest points as a close approximation.
Should I round up on bags?: Yes, and this tool already does. Compost settles and spreads unevenly, so having a spare bag is better than coming up short.
What size are compost bags?: Most bagged compost is 1, 1.5, or 2 cubic feet. Check your bag and enter that number so the bag count matches what you'll actually buy.