Compost Recipe & Browns to Add to Your Greens
Balances greens
Enter your greens and the carbon and nitrogen content of each material to get the browns to addand the achieved C:N — so your pile hits the 25–30:1 sweet spot, decomposes fast and never smells.
Balance your compost
Next: mix 100 kg greens with 117 kg browns (217 kg total) to land at C:N 30.
Real feedstock C and N vary widely; weigh damp materials and adjust by feel — the pile should be moist like a wrung sponge and heat up within days if the C:N is near 25–35.
Compost recipe — key facts
- Target C:N
- ≈ 25–30:1 to start
- Too much carbon
- slow, barely heats
- Too much nitrogen
- smelly, slimy
- Greens C:N
- low, ≈ 10–25:1
- Browns C:N
- high, 40:1 and up
- Moisture
- wrung-out sponge, ~50–60%
- Mature compost
- settles to ~10–15:1
- Privacy
- Runs in your browser; nothing uploaded
Get the carbon-to-nitrogen balance right and the pile does the rest
Good compost is a balancing act between carbon and nitrogen. Microbes burn carbon-rich browns for energy and use nitrogen-rich greens to build their bodies, and they work best when those two are in balance at a starting C:N of around 25–30:1. Too much carbon and the pile barely heats, sitting for months almost unchanged; too much nitrogen and it turns slimy, smelly and anaerobic. A compost recipe settles it with numbers — how much carbon and nitrogen each material brings, and how many browns to add to land in the sweet spot.
This tool gives the browns needed, the total mix size and the achieved C:N from your greens and each material's carbon and nitrogen content. Use it to blend a fast, sweet-smelling pile, soak up excess nitrogen with the right amount of browns, and stop guessing at the ratio. Pair it with the Compost C:N Ratio, Compost & Manure and Vermicompost tools for a full composting plan.
Hit the sweet spot
Blend to a 25–30:1 C:N for a fast pile.
Stop the smell
Add enough browns to soak up nitrogen.
Speed decomposition
Balanced carbon and nitrogen heats the pile.
Use what you have
Works with any greens and browns on hand.
Frequently Asked Questions
What is a compost recipe calculator?+
It works out the right blend of carbon-rich 'browns' and nitrogen-rich 'greens' for a compost pile. You enter how much of each material you have along with its carbon and nitrogen content, and it tells you how many browns to add to your greens to hit a target carbon-to-nitrogen (C:N) ratio, the total size of the mix, and the C:N you actually achieve.
What C:N ratio should compost start at?+
Aim for a starting C:N of roughly 25–30:1. Microbes use carbon for energy and nitrogen to build their bodies, and that range feeds them in balance so the pile heats quickly and breaks down efficiently. As composting finishes, the C:N naturally drops toward 10–15:1 in the mature compost.
What happens if there's too much carbon?+
Too many browns (a high C:N, say above 40:1) starves the microbes of nitrogen, so the pile barely heats and decomposes very slowly — it can sit for many months almost unchanged. The fix is to add more greens or a nitrogen source to bring the ratio back toward 25–30:1.
What happens if there's too much nitrogen?+
Too many greens (a low C:N, below about 20:1) leaves excess nitrogen the microbes can't use, so it escapes as ammonia — the pile turns slimy, smelly and can go anaerobic. Adding browns such as dry leaves, straw, cardboard or sawdust soaks up that nitrogen and stops the smell.
What count as greens and browns?+
Greens are fresh, moist, nitrogen-rich materials: grass clippings, vegetable scraps, manure, coffee grounds, fresh weeds. Browns are dry, carbon-rich materials: dead leaves, straw, cardboard, paper, sawdust, woodchips. Greens have a low C:N (roughly 10–25:1); browns are high (40:1 up to several hundred:1 for sawdust).
How does the calculator hit the target?+
It uses the carbon and nitrogen content of each material to track total carbon and total nitrogen in the mix. It then adds browns until the combined carbon-to-nitrogen ratio reaches your target, and reports the browns needed, the total mix size and the achieved C:N so you can see how close you land.
Does moisture matter as well as C:N?+
Yes. Even a perfect C:N won't compost if the pile is too dry or too wet — aim for the dampness of a wrung-out sponge (around 50–60% moisture). Browns also add structure and air gaps; turning the pile keeps oxygen flowing. C:N gets the chemistry right, but moisture and air finish the job.
Can I use it for any materials?+
Yes — enter the carbon and nitrogen percentages for whatever feedstocks you have, whether that's manure and straw, kitchen scraps and cardboard, or grass and leaves. The dry-matter carbon and nitrogen approach is universal, so you can blend any combination and still target a balanced C:N.
Are the figures precise?+
They're solid planning figures. Real materials vary in carbon, nitrogen and moisture, and the C:N shifts as the pile breaks down. Use the recipe as a starting blend, then read the pile: if it's slow and cool add greens, if it smells add browns. Composting is about steering, not exact prediction.