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Compost Bin Volume Calculator

Enter the bin dimensions, fill level and material density to see its volume and capacity.

How it is calculated

The tool treats the bin as a rectangular box. Enter length, width and height in metres, the fill level as a percentage of the bin you will actually load (1 to 100), and the density of the material in kilograms per cubic metre. It computes volume = length × width × height in m³, litres as volume × 1,000, usable volume = volume × fill / 100, and weight = usable volume × density in kg. Use inside dimensions, since the walls take up space. Round or irregular bins are not supported, so for a round bin calculate an equivalent volume yourself. Density varies a lot between fresh waste, part-rotted and finished compost, and with moisture.

Worked example

A bin 1.2 m long, 0.9 m wide and 1 m high, filled to 80 %, with material at 500 kg/m³. Volume = 1.2 × 0.9 × 1 = 1.08 m³, which is 1,080 L. Usable volume = 1.08 × 0.80 = 0.864 m³, or 864 L. Weight = 0.864 × 500 = 432.0 kg of material. The headroom left (216 L) is what you need to turn and aerate the pile.

Try this example →

Common mistakes

  • Entering dimensions in centimetres: the fields are in metres, so 120 instead of 1.2 gives a volume 1,000,000 times too large.
  • Using outside dimensions of a bin with thick timber walls, which overstates the space inside.
  • Filling to 100 % and leaving no room to turn the heap: that is why a fill percentage is asked for.
  • Treating the weight as exact: the density depends on the material and its moisture, and it changes as the pile decomposes and shrinks.
  • Expecting finished compost to equal the bin volume: the pile reduces in volume as it rots.

About this calculator

A compost bin's usable capacity is its geometric volume — length × width × height for a rectangular bin — multiplied by how full you intend to fill it, since compost needs headspace for turning and aeration. Converting that volume to a weight requires the bulk density of the material being composted, which typically runs around 500–700 kg per cubic meter for active, part-decomposed compost, though fresh green waste and finished compost differ noticeably.

Home gardeners and allotment growers use this calculation when choosing a bin size for their household's food and garden waste output, or when working out how much finished compost a given bin will yield for spreading on beds. Undersizing a bin means waste piles up faster than it breaks down; oversizing it wastes space and can slow decomposition if the pile never builds enough mass to heat properly.

This calculator takes your bin dimensions, fill level and material density, and returns the bin's volume and how much material it can hold. It is built for rectangular bins; for a round bin, enter its base area (π × radius²) as the length and 1 m as the width.

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