Washington State University

Organic Farming Systems and Nutrient Management

Compost Mixture Calculator version 2.1

The Compost Mix Calculator (click to download Excel file) is a spreadsheet that calculates compost mixture C:N ratio and moisture content, based on the analysis of your feed stocks and the mixture proportions that you choose. You can use the spreadsheet evaluate the effects of different feedstock mixtures on C:N ratio and moisture content of the initial pile. You can also use the spreadsheet to check if the materials you have on hand will make a suitable mix for composting, or if you need to find different materials or change proportions.

The spreadsheet consists of three different worksheets. The first is a list of typical feed stock characteristics taken from the On-Farm composting Handbook (Rynk et al, 1992), and from data that we have collected at WSU-Puyallup. The second page is the compost mixture input sheet where you enter your feedstocks and change proportions to come up with your own mixture. The third page does the calculations to make the calculator operate.

The compost mixture input sheet contains input cells for entering feedstock information, and protected cells that show the calculated results. Enter feedstock information based on your own analyses or data, or use the information provided in the feedstock list. The calculator then calculates the moisture content and C:N ratio of your compost mixture. Mixtures are calculated by volume, not by weight. If you need to convert between weight and volume you can use the bulk density data provided in the feedstock list. You can change the proportions and types of feedstocks in your calculation until you find the desired C:N ratio and moisture content.


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