Garden & Water Utilities
Compost C:N Ratio Calculator
Estimate the blended carbon-to-nitrogen ratio of a compost mix from two materials. Amounts and C:N assumptions are editable, so you can use kg or lb and the ratios from your own feedstock or lab report.
How the estimate works
The calculator converts each ingredient's stated C:N ratio into estimated carbon and nitrogen fractions, weights those fractions by the entered material amounts, and divides total carbon by total nitrogen. The University of Minnesota Extension describes about 25:1 to 30:1 as an optimal composting range; moisture, oxygen, particle size and pile management still matter.
Source: University of Minnesota Extension, “Aged manure is not composted manure”.