Compost Mix Calculator
Browns needed for a 30:1 pile from any greens weight.
What it does
Compost microbes burn carbon for energy and spend nitrogen building bodies, fastest near 30 parts carbon to 1 part nitrogen by weight. Wetter nitrogen rich greens plus dry carbon browns in the right share keep piles hot without ammonia stink.
The tool above takes the green material with its weight and the brown material. It returns the brown kilos for a 30:1 mix with the total pile weight beside it.
The default 10 kg of grass clippings (19:1) with leaves (60:1) needs 3.67 kg of leaves for 13.67 kg total. Paper at 170:1 needs far less per kilo, which is why thin browns stretch across big grass loads.
Ratios and the 30:1 target follow Cornell composting references with USDA composting guidance behind them. Both note the same caveats: woody carbon resists breakdown, so real piles run a little high on carbon by design.
How to use
- Pick the green material closest to yours.
- Pick the brown material you have on hand.
- Weigh the greens in kilos.
- Read the brown kilos first for the mix.
- Layer, wet, and turn when the core cools.
Formula
- green ratio
- C:N of the nitrogen rich input, below 30.
- brown ratio
- C:N of the carbon input, above 30.
- 30:1
- Target carbon to nitrogen by weight.
Greens at or above 30 and browns at or below 30 are rejected, since no positive mix reaches target from there. Shredded inputs compost faster than the same weight in chunks.
Worked example
Example: 10 kg grass with leaves
Defaults: grass 19:1, leaves 60:1, 10 kg greens.
- Gap below: 30 - 19 = 11.
- Gap above: 60 - 30 = 30.
- Browns: 10 x 11 / 30 = 3.67 kg.
- Total: 10 + 3.67 = 13.67 kg at 30:1.
- Tool shows 3.67 kg, 13.67 kg, 30:1.
Reference table
| Material | Ratio | Side |
|---|---|---|
| Food scraps | 15:1 | Green |
| Grass clippings | 19:1 | Green |
| Leaves | 40-80:1 | Brown |
| Paper | 170:1 | Brown |
| Wood, sawdust | 300-700:1 | Brown |
Limits
- Simplified ratios; real materials vary by batch.
- Woody carbon resists, so piles run carbon heavy.
- Moisture and air matter as much as the ratio.
- Meat and dairy need hot managed systems.
Common mistakes
- Mixing by volume instead of by weight.
- Counting finished compost as a brown.
- Drowning the pile past wrung sponge dampness.
- Never turning until it goes anaerobic.
- Adding meat to a cold backyard pile.
Try it yourself
Quick checks. Answers sit tucked under each question.
5 kg scraps (15) with paper (170)?
5 x 15 / 140 = 0.54 kg of paper.
10 kg manure (20) with straw (70)?
10 x 10 / 40 = 2.5 kg of straw.
Ratio check on the example?
(10x19 + 3.67x60) / 13.67 = 410 / 13.67 = 30:1.
Questions
What is the best compost ratio?
About 30 parts carbon to 1 nitrogen by weight.
How much brown for grass?
10 kg grass needs 3.67 kg leaves by this math.
Why does my pile stink?
Excess nitrogen or water: add browns and turn for air.
Why is my pile cold?
Too much carbon or too dry: add greens and water.
Leaves or paper for browns?
Both work; paper needs far less weight per green kilo.
How wet should it be?
Wrung sponge damp: drops on squeezing, no dripping stream.