Making and Using Compost
40 | Unit 1.7
Appendix 4: Calculating C:N Ratios for Compost
- A Rough Guide
you have 5 pounds of grass clippings (C:N ratio = 20:1).
you have 5 pounds of leaves (C:N ratio = 40:1).you have a total of 10 lbs. of material:
1/2 (50%) are grass, 1/2 (50%) are leaves.Multiply the % of grass by the C:N ratio of grass, add the multiplication of the %
of leaves by the C:N ratio of leaves:
(50% X 20/1) + (50% X 40/1) =
10 + 20 = 30 ---> which in fraction notation is 30/1 or 30:1.The C:N ratio is 30:1. (*Optimal C:N Ratio is 25–30:1)
Adapted from “Calculation of Carbon-to-Nitrogen Ratio (C:N)” by Master Composter, available online at
http://www.mastercomposter.com. See also: http://compost.css.cornell/edu/calc/cn_ratio.html
Appendix 4