Composting Time Calculator

Work out composting time instantly with clear inputs, formula shown and shareable results.

About Composting Time Calculator

The estimate starts from eight weeks for an ideal 30:1 pile turned weekly, penalising deviation from that ratio, longer intervals between turnings and piles under three quarters of a cubic metre. Piles smaller than about a cubic metre cannot hold heat, which is why a small bin composts far more slowly than the same material in a large heap.

Formulas

Time estimate

weeks = 8 x C:N penalty x turning factor x size penalty

Volume reduction

finished volume is about 40% of the starting volume

Worked example

With the default values below, Composting Time Calculator returns Estimated time to finished compost of 8.16. Change any input above and every figure here is recalculated in your browser.

Inputs used

Carbon to nitrogen ratioaccepts 5–100: 30
Days between turningsminimum 1: 7
Pile volumeminimum 0.01 m3: 1 m3

Results

Estimated time to finished compost: 8.16 weeks
Time in days: 57
Turnings over that period: 8
Finished compost volume: 0.400 m3

Step by step

1Values used
2Time estimate
3Volume reduction
4Estimated time to finished compost= 8.16 weeks
5Time in days= 57
6Turnings over that period= 8
7Finished compost volume= 0.400 m3

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Composting Time figure worked out?

weeks = 8 x C:N penalty x turning factor x size penalty. The estimate starts from eight weeks for an ideal 30:1 pile turned weekly, penalising deviation from that ratio, longer intervals between turnings and piles under three quarters of a cubic metre.

Why does this matter?

Piles smaller than about a cubic metre cannot hold heat, which is why a small bin composts far more slowly than the same material in a large heap.

What do I need to enter?

Enter carbon to nitrogen ratio, days between turnings, pile volume. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.