Compost Calculator - Technical Details
The Compost Calculator takes the quantity of each material that you provide and calculates the carbon/nitrogen ratio of the resulting combination based upon approximate ratios for each of the materials.
C/N Ratios: We are using the following carbon/nitrogen values for each ingredient:
| Material | Carbon | Nitrogen | C/N Ratio |
| Alfalfa (hay, dry) | 40.000 | 2.250 | 17.778 |
| Alfalfa (pellets) | 40.500 | 2.700 | 15.000 |
| Blood meal | 43.000 | 13.000 | 3.308 |
| Cardboard (dry) | 40.000 | 0.100 | 400.000 |
| Coffee grounds | 25.000 | 1.000 | 25.000 |
| Cottonseed meal | 42.000 | 6.000 | 7.000 |
| Fruit waste | 8.000 | 0.500 | 16.000 |
| Grass (hay, dry) | 40.000 | 1.250 | 32.000 |
| Grass clippings (fresh) | 12.500 | 1.500 | 8.333 |
| Kitchen waste | 15.000 | 1.500 | 10.000 |
| Leaves (dead) | 27.500 | 0.700 | 39.286 |
| Manure (cattle, fresh) | 16.000 | 0.800 | 20.000 |
| Manure (chickens-broiler, fresh) | 26.250 | 1.650 | 15.909 |
| Manure (chickens-laying, fresh) | 15.250 | 1.800 | 8.472 |
| Manure (horse, fresh) | 27.500 | 0.750 | 36.667 |
| Newspaper (dry) | 40.000 | 0.100 | 400.000 |
| Oat straw (dry) | 48.000 | 0.500 | 96.000 |
| Sawdust | 37.500 | 0.100 | 375.000 |
| Seaweed (fresh) | 10.000 | 1.000 | 10.000 |
| Soybean meal | 42.000 | 6.000 | 7.000 |
| Vegetable waste (leafy, fresh) | 10.000 | 1.000 | 10.000 |
| Vegetable wastes (starchy) | 15.000 | 1.000 | 15.000 |
| Weeds (fresh) | 15.000 | 2.500 | 6.000 |
| Wheat straw (dry) | 48.000 | 0.500 | 96.000 |
The Calculation: For each ingredient we:
- Calculate the carbon value: (Quantity of ingredient) X (Carbon Value of ingredient) = Carbon Value
- Calculate the nitrogen value: (Quantity of ingredient) X (Nitrogen Value of ingredient) = Nitrogen Value
- Total all the carbon values to get Total Carbon Value
- Total all the nitrogen values to get Total Nitrogen Value
- Calculate the C/N ratio: C/N Ratio = Total Carbon Value/Total Nitrogen Value
Here is an example:
Ingredients:
10 buckets of horse manure with a carbon value of 27.5 and a nitrogen value of 0.75
2 buckets of dried grass with a carbon value of 40 and a nitrogen value of 1.25
Carbon Value:
Carbon Value from horse manure = 27.5 X 10 = 275
Carbon Value from dried grass = 40 X 2 = 80
Total Carbon Value = 275 + 80 = 355
Nitrogen Value:
Nitrogen Value from horse manure = 0.75 X 10 = 7.5
Nitrogen Value from dried grass = 1.25 X 2 = 2.5
Total Nitrogen Value = 10
C/N Ratio:
Carbon/Nitrogen = 355/10 = 36 (these numbers are approximate, so rounding is fine)
This example mix is just a tiny bit over our desired maximum value of 35.0. That means it needs a little less carbon or a bit more nitrogen.
Say we add 1/4 bucket of blood meal. This will increase the carbon by 43 X 0.25 = 10.75 and the nitrogen by 13 X 0.25 = 3.25. Our new values will be Total Carbon = 366 and Total Nitrogen = 13. Our new ratio is 366/13 = 28. That's nicely in the range we want (25 - 35) and should produce great compost.