Compost carbon to nitrogen calculator
Compost works best around 30 parts carbon to one of nitrogen. Too much nitrogen smells; too much carbon does nothing.
Straw 80; dry leaves 60; sawdust 400; cardboard 350.
%
Grass clippings 17; kitchen scraps 15; manure 20; coffee grounds 20.
%
Carbon to nitrogen ratio
30.00
- Total mix
- 100.0
- Carbon material for the target ratio
- 60.0
- Carbon material to add Negative means you have too much already.
- 0.0
- Total carbon
- 39.00
- Total nitrogen
- 1.300
Show the working
- Carbon-rich material = 60
- Its C:N ratio = 80
- Its nitrogen content = 0.5
- Nitrogen-rich material = 40
- Its C:N ratio = 15
- Its nitrogen content = 2.5
- Target C:N ratio = 30
- brown_n_mass = 60 * 0.5/100 = 0.3
- green_n_mass = 40 * 2.5/100 = 1
- brown_c = 0.3 * 80 = 24
- green_c = 1 * 15 = 15
- Total nitrogen = 0.3 + 1 = 1.3
- Total carbon = 24 + 15 = 39
- Carbon to nitrogen ratio = 1.3 > 0 ? 39 / 1.3 : 0 = 30
- Total mix = 60 + 40 = 100
- Carbon material for the target ratio = (80 - 30) * 0.5/100 != 0 ? 1 * (30 - 15) / ((80 - 30) * 0.5/100) : 0 = 60
- Carbon material to add = 60 - 60 = 0
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- nitrogen mass = material mass x nitrogen percentage
- carbon mass = nitrogen mass x that material C:N ratio
- mix ratio = total carbon / total nitrogen
Moisture matters as much as the ratio: aim for the dampness of a wrung-out sponge, around 50 to 60% water.