Online Tool Store
Compost Ratio Calculator
Balance a compost heap's carbon to nitrogen ratio from the materials you have, and see what to add to reach the range that heats properly.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Fun & Misc
Compost Ratio Calculator
Frontend preview — no upload or external service.
Mix result
8 kg of kitchen scraps (C:N about 15:1) with 6 kg of dry leaves (60:1) gives roughly 34:1 — add 2 kg more greens to reach the 30:1 target.
How the Compost Ratio Calculator works
- Weigh or estimate what you have in greens and browns; volume estimates are fine if you are consistent.
- Compare the resulting ratio to the 25:1 to 30:1 target where heaps heat reliably.
- Add the recommended material, mix thoroughly, and check moisture — ratio alone will not heat a dry heap.
The method
Composting microbes consume carbon for energy and nitrogen for protein, and the mix works best when carbon outweighs nitrogen by roughly thirty to one by mass.
C:N = Σ(mass x carbon fraction) / Σ(mass x nitrogen fraction)
Kitchen scraps sit near 15:1 and dry leaves near 60:1, so roughly equal masses land near 30:1 — the range where a heap heats rather than smells.
FAQ
Why does my heap smell of ammonia?
Too much nitrogen. Excess nitrogen is driven off as ammonia, which is both the smell and a waste of the nutrient. Add browns and turn the heap.
Why is nothing happening at all?
Usually too much carbon, too little moisture, or too small a heap. Below roughly a cubic metre a heap loses heat faster than it generates it.
Does the ratio need to be exact?
No. Anywhere from 25:1 to 35:1 works. The ratio matters far less than moisture like a wrung-out sponge and enough air to keep it aerobic.
How we compare
| Feature | Online Tool Store | Doing it by hand | A single-purpose app |
|---|---|---|---|
| Per-material C:N values | ✓ | Guesswork | Yes |
| Tells you what to add | ✓ | ✗ | Sometimes |
| No sign-up | ✓ | ✓ | ✗ |
| Covers moisture and aeration | ✓ | Varies | ✓ |
Compost Ratio Calculator gets the mix into the right range, then says plainly that moisture and heap size decide whether it actually heats.