Compost Mix Calculator: Greens and Browns
Add what you’re putting in your compost, in buckets, bags or any other unit. The calculator checks the balance of greens and browns by volume and tells you what to add to reach about 2–3 parts browns to 1 part greens.
On this page
The calculator
Add a few materialsSee result ↓Compost mix check · hopcompost.com/compost-calculator/
Add a few materials to check your mix.
Use the + buttons or type amounts. Any unit works, as long as you use the same one for everything.
Advanced: the numbers
Browns to greens by volume: no mix yet.
| In your mix | Amount | Type | C:N (approx.) |
|---|---|---|---|
| Nothing added yet. | |||
Target: about 2–3 parts browns to 1 part greens, which lands most mixes near 25–30:1 carbon to nitrogen. C:N figures are published approximate ranges; real materials vary.
How it works
Compost microbes need carbon for energy and nitrogen to grow. Carbon comes from dry browns such as leaves, cardboard and straw. Nitrogen comes from wet greens such as food scraps, coffee grounds and grass clippings. The balance that works best is roughly 2 to 3 parts browns to 1 part greens by volume.
The calculator adds up your browns and your greens and compares them. If there's less than about 2 parts browns per part greens, it tells you how much brown material to add to reach 2.5 to 1. If there's more than about 3.5 parts browns, it tells you how many greens to add. It uses the same unit you chose, so the answer reads like "about 3 more buckets".
It works by volume because that's how people add material, and because greens are heavier and wetter than browns. A volume ratio of 2–3 to 1 already accounts for that difference for common household materials.
Reading your result
| Browns : greens | What it means | What you'll notice | Fix |
|---|---|---|---|
| Under 1.5 : 1 | Too wet (nitrogen-heavy) | Slimy, smells of ammonia or rot, flies | Add browns, turn |
| 1.5–2 : 1 | A bit wet | Heats fast, may smell after rain | Add a little browns |
| 2–3.5 : 1 | Balanced | Warm, earthy, shrinking steadily | Keep it damp and turn |
| 3.5–5 : 1 | A bit dry | Slow, stays cool | Add a few greens, water |
| Over 5 : 1 | Too dry (carbon-heavy) | Nothing happens for months | Add greens, water well |
Numbers aside, trust the pile. If it's warm in the middle, damp like a wrung-out sponge and smells earthy, it's working. If it smells, see why compost smells. Not sure whether something belongs in the pile at all? Check the A–Z list.
Frequently asked questions
What is the best ratio of browns to greens?
About 2 to 3 parts browns to 1 part greens by volume. That puts a typical mix near a carbon-to-nitrogen ratio of about 25–30:1, which is what most university extension guides recommend.
Why measure by volume and not weight?
Because that’s how you add things: buckets, bags and wheelbarrows. Greens are heavier and wetter than browns, so a volume ratio of 2–3:1 browns to greens works out close to the ideal carbon-to-nitrogen balance for common materials.
What happens if my compost has too many greens?
It gets wet, dense and smelly, often with an ammonia or rotten-egg smell, because nitrogen escapes and air can’t get in. Mix in dry browns like shredded leaves or cardboard and turn it. See why compost smells.
What happens if my compost has too many browns?
Nothing much, and that’s the problem: a brown-heavy pile stays dry and cool and can take a year or more. Add greens such as kitchen scraps, coffee grounds or grass clippings, and water it.
Is the calculator accurate?
It’s a rule-of-thumb check, not a lab test. Real materials vary a lot in moisture and nitrogen. If the pile heats up a little, smells earthy and stays damp, your mix is right whatever the numbers say.
Are coffee grounds green or brown?
Green. They look brown but are rich in nitrogen, at about 20:1 carbon to nitrogen. More on coffee grounds.