Compost Bin Size and Yield Calculator

How it works

A square or rectangular bin holds length × width × height; a round bin made from a wire hoop or a barrel holds π × radius² × height. The height is the height of the material in it, so a bin with 4 ft walls filled to 3 ft holds a 3 ft pile.

Extension composting guides give about 3 ft × 3 ft × 3 ft, or 1 cubic yard (27 cu ft), as the smallest pile that holds enough heat to compost hot: NC State's Extension Gardener Handbook (AG-831, 2022) says 27 cubic feet, 3 feet wide, deep and tall, and Colorado State Extension's fact sheet 7.212 (1997, reviewed 2025) says around 36 by 36 by 36 inches. The calculator checks both the volume and that no side, diameter or height is below 3 ft, because a long, thin or shallow pile of the right volume loses heat through its larger surface.

As material breaks down it loses water, carbon dioxide and air space, and the pile shrinks. Colorado State's fact sheet says composting reduces yard waste volume by 50 to 75 percent, and NC State's handbook says a pile may be about half its original volume after a month. The finished share is therefore an input, defaulting to a typical 40%. The raw-material share of the bin shows how full that material makes the bin.

Formula

box volume       = length × width × height
round volume     = π × (diameter ÷ 2)² × height
cu yd            = cu ft ÷ 27
hot-compost size = volume ≥ 27 cu ft and every dimension ≥ 3 ft
finished compost = raw volume × finished % ÷ 100

Example

A 3 ft × 3 ft bin filled 3 ft deep holds 27 cu ft, exactly 1 cu yd, and meets the minimum. Filled with 1 cu yd of raw material that finishes at 40% of its volume, it makes 10.8 cu ft, or 0.40 cu yd, of compost.

A round wire bin 4 ft across with a 3 ft pile holds π × 2² × 3 = 37.7 cu ft (1.40 cu yd) and meets the minimum. A 3 ft hoop with a 3 ft pile holds only 21.2 cu ft and falls short.

Assumptions and limitations

• The bin is a straight-sided box or cylinder. A free-standing heap with sloping sides holds less than a box of the same footprint and height.
• The 3 × 3 × 3 ft minimum is a rule of thumb from extension composting guides, not a sharp threshold; moisture, the carbon-to-nitrogen balance and turning matter as much as size. Colorado State notes that well-insulated wood or plastic bins can be smaller and still hold enough heat, and some guides give larger minimums for open heaps.
• The finished share is an editable typical value. Published figures range from about 25% to 50% of the raw volume (Colorado State: a 50 to 75 percent reduction), and actual shrinkage depends on the materials and on how long the compost is left.
• Volumes of loose material depend on how tightly it is packed; the same leaves can fill very different volumes loose or compressed.

Frequently asked questions