http://www.organicgardening.com/featureprint/1,7759,s1-5-21-112,00.html
Put your math skills to work and figure out if your compost has a balanced carbon to nitrogen ratio.
The carbon/nitrogen ratio
If you are a compost nerd, you might already know that the ideal ratio of carbon to nitrogen in a compost pile is about 30:1. A pile with that balance of materials will rot steadily, and it will yield nutrient-rich compost.
But how do you know what your pile's ratio is? "The most important factor in estimating the carbon-to-nitrogen ratio is how much water is present," explains Eric Evans, Ph.D., laboratory director of Woods End Research Laboratory in Mt. Vernon, Maine. "Dry materials are generally in the range of 40 to 50 percent carbon, and sloppy, wet materials are generally 10 to 20 percent carbon." Here are the specifics on many common materials. After you've scanned through these, you'll see how to calculate your pile's exact Carbon/Nitrogen ratio.
Do the math
To calculate the carbon-to-nitrogen of your compost mix, use the chart above to find the approximate percentages of carbon and nitrogen in your ingredients. Even if you're unlikely to weigh every ingredient you add to your heap, this formula will give you an idea of how to adjust the proportions of materials in your pile to get finished compost more quickly.
1. Calculate your pile's Total Carbon Value by multiplying the percent carbon of each ingredient by the number of parts (by weight) of that ingredient and then adding up the carbon totals for all the ingredients
2. Do the same for the nitrogen.
3. Divide the carbon by the nitrogen to get the C:N ratio. If it's between 25 and 35, your pile should compost beautifully. If the ratio is higher or lower than that, adjust the proportions of ingredients to bring it into the range of 25 to 35 parts carbon for each one part nitrogen.
Here's an example of how the carbon-to-nitrogen ratio works when you apply the formula to real-life amounts of real-life compost ingredients:
Starting with 50 pounds of nonlegume hay, 10 pounds of kitchen scraps, and 2 pounds of coffee grounds:
50 lbs hay x 40% C = 20 lbs. C
10 lbs kitchen scraps x 10% C = 1 lb. C
2 lbs coffee grounds x 25 % C = 0.5 lb. C
20 + 1 + 0.5 =21.5 Total Carbon Value
50 lbs hay x 1% N = 0.5 lb. N
10 lbs kitchen scraps x 1% N = 0.1 lb N
2 lbs coffee grounds x 1 % N = 0.02 lb. N
0.5 + 0.1 + 0.02 = 0.62 Total Nitrogen Value
21.5/0.62= 34.7 parts carbon to 1 part nitrogen
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