Compost Mix Calculator
Bernalillo County Extension Master Composters
When adding materials to your compost, it is not necessary to use precise measurements. You can build excellent compost without using a calculator. Few people use one. However, if you wish to better understand the C:N (carbon / nitrogen) ratio or if you just like being very precise, you might have fun using this calculator to calculate the C:N ratio of your compost. The calculator is an Excel spreadsheet built by Omar Sadek, graduate of our Spring 2011 Master Composter class.
- Carbon / Nitrogen Ratio Simplified Calculations (slides from talk given by Omar)
Omar used information from the following links while building the calculator:
- Washington State University, Whatcom County Extension: Compost Fundamentals
- Cornell Waste Management Institute: On-Farm Composting Handbook
- The Humanure Handbook: The Carbon / Nitrogen Ratio
- Colorado State University Extension: Organic Materials as Nitrogen Fertilizers
- Government of Alberta, Agriculture and Rural Development: Manure Composting Manual
- British Columbia, Ministry of Agriculture and Food: Characteristics of On-Farm Composting Materials
Omar said that most numbers were obtained through various on-line reference sources such as Cornell's On-Farm Composting Handbook, Appendix A, Table A.1. In many cases, he found a wide range of values for the same material. For example, the C:N ratio for wood chips (soft wood) ranged from 226 to 641 depending on the source of the info. For the most part, he used values listed in the BCEMC Spring 2011 master composter manual. If a material was not listed in the manual, he picked an average value based on the identified range. Where numbers were not readily available, he derived them himself. For example, he weighed 5 gallons of the material and extrapolated up to the corresponding cubic yards for bulk density or he combined similar ingredients where appropriate (e.g., rabbit manure has a similar nitrogen content as sheep manure). To simplify the calculations when dealing with fertilizers, he assumed a standard carbon content of 40% for the green / brown material entered into the calculator. Also, given our dry climate in New Mexico, he did not include moisture content in any of the calculations as that would introduce even more variability / guess-work into the computations.