🌱 Compost Calculator
Get your green-to-brown balance right. Enter the nitrogen-rich and carbon-rich materials you're adding and see your estimated C:N ratio, whether it's in the sweet spot, and how much to add to balance the pile.
⚖️ Balance your pile
🌱 Your compost blend
Estimates only. C:N constants are rule-of-thumb averages; real materials vary with moisture, source, and how finely they're chopped. Aim for the range, then let sight and smell guide you.
What is a Compost Calculator?
It's a tool for getting the single most important compost variable right: the ratio of carbon to nitrogen. Composting microbes eat carbon for energy and nitrogen to build protein, and they thrive at roughly 25–30 parts carbon to every part nitrogen. Enter the materials you're piling up — greens like food scraps and grass, browns like dry leaves and cardboard — and the calculator estimates your blend's C:N ratio and tells you whether it's balanced.
When the pile is off, it tells you how to fix it: how much brown to add to a wet, nitrogen-heavy heap, or how much green to add to a dry, carbon-heavy one. It also estimates the rough volume your materials fill, so you can size a bin or tumbler. Get the balance right and your kitchen scraps turn into finished compost faster, with less smell and less waste sent to landfill.
❓ Frequently Asked Questions
What is the ideal carbon-to-nitrogen (C:N) ratio for compost?
Composting microbes work fastest at a carbon-to-nitrogen ratio of about 25–30 parts carbon to 1 part nitrogen. Too much nitrogen (too many greens) makes the pile wet and smelly; too much carbon (too many browns) makes it dry and slow to heat. This calculator estimates your blend's ratio and tells you which way to nudge it.
What counts as a green versus a brown?
Greens are moist, nitrogen-rich materials: fresh food scraps, grass clippings, coffee grounds, and manure. Browns are dry, carbon-rich materials: autumn leaves, straw, cardboard, and shredded paper. The names describe their role in the pile, not their colour — coffee grounds are brown in colour but count as a green.
How does the calculator estimate the blend ratio?
It uses the Cornell aggregate method: each material carries a documented C:N ratio and an approximate nitrogen content, so the tool sums the total carbon and total nitrogen across everything you add and divides. That is more accurate than simply averaging the ratios, because a material's contribution depends on how much nitrogen it actually brings.
Should I measure by weight or by volume?
Weight is more accurate because the C:N math is based on mass. Any consistent unit works (kg or lb) since only the ratio matters. If you'd rather eyeball volumes, a common rule of thumb is roughly 2–3 parts browns to 1 part greens by volume — use this tool to sanity-check that against the materials you actually have.
Are these numbers exact?
No — treat them as guidance. Published C:N values are averages; real materials vary with moisture, source, and how finely they're chopped. Aim for the ideal range, then let your senses guide you: a healthy pile smells earthy, feels like a wrung-out sponge, and heats up in the middle.