Compost Ratio Calculator
A compost heap that will not heat up almost always has the wrong balance. Too much green material and it goes wet, dense and smells of ammonia; too much brown and it simply sits there for a year doing nothing. The target is roughly twenty-five to thirty-five parts carbon to one of nitrogen, and the useful thing to know is how enormously the materials differ — cardboard is so carbon-rich that a little balances a great deal of grass.
What this generator does
Takes a mix of materials with their individual carbon-to-nitrogen ratios and the parts of each, computes the parts-weighted blend, and reports whether that lands inside the range where a heap breaks down properly.
How to use this tool
- Choose how many materials are in the mix.
- Read each material's own ratio and how many parts of it there are.
- Check the blended figure against the target range.
- Note how few parts of cardboard it takes to balance a lot of grass.
Understanding the controls
- How many materials
- Between 2 and 5, drawn from common garden and kitchen materials whose ratios differ by more than twenty-fold.
- Seed
- Any word reproduces exactly the same materials and proportions.
Common use cases
- Diagnosing a heap that will not heat up or smells wrong
- Balancing a load of grass clippings with something brown
- Teaching the carbon-to-nitrogen idea with real materials
- Planning what to add before emptying the shredder into the heap
- Setting the same mix twice from a seed
How this generator works
The blend is a weighted mean rather than a plain average, which matters enormously here: three parts of something at twenty and one part at a hundred gives forty, not sixty. The check confirms the blend recomputes and that it falls between the smallest and largest ratio in the mix — a weighted mean always must, and a blend outside that range would mean the arithmetic had gone wrong.
Randomness and fairness
The materials and their proportions are random; the blended ratio is exact arithmetic on them. A seed reproduces the same mix exactly and is therefore explicitly not cryptographically secure. Without a seed the browser's cryptographically secure generator is used.
For how randomness is produced across the whole site, see how Generate Random works.
Limitations and good to know
- Ratios are typical published figures; real material varies a great deal with age, moisture and source.
- Parts are treated as comparable by volume, whereas the ratio is properly a matter of dry weight.
- Air and moisture matter as much as the ratio. A correctly balanced heap that is compacted or bone dry will still do nothing.
- Nothing here addresses what should not go in a heap at all — cooked food, perennial weed roots, diseased material.
- Mixes are not stored between visits; seed one you want again.
Privacy and your data
The blend is computed in your browser. Nothing about the mix or your seed is transmitted or kept.
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