Compost Calculator

Estimate your compost pile's carbon-to-nitrogen (C:N) ratio from the weight of your brown (carbon-rich) and green (nitrogen-rich) materials, and see how close your mix is to the ideal 25-30:1 range for fast, low-odor decomposition.

Quick Facts

Ideal C:N ratio
25-30 parts carbon to 1 part nitrogen
The range most composting guides recommend for fast, aerobic, low-odor breakdown.
Method
Weight-weighted average of each material's typical C:N ratio
Combined ratio = (browns weight × browns C:N + greens weight × greens C:N) ÷ total weight.

Results

Calculated
Combined C:N Ratio
—
Weighted-average ratio of your mix
Total Mix Weight
—
Browns + greens combined
Browns Share
—
Percent of mix by weight that's carbon-rich
Suggested Adjustment
—
Approx. amount to reach ~27.5:1

Ready

Enter your browns and greens, then press Calculate.

How to use this calculator

Pick the type of brown (carbon-rich) material you're adding and enter its weight in pounds, then do the same for your green (nitrogen-rich) material. Click Calculate to see the combined carbon-to-nitrogen (C:N) ratio of your mix, along with the total weight, the browns' share of the pile, and roughly how much to add to reach the ideal range. Click Clear to reset all fields and start a new calculation.

The formula

Every organic material has a typical carbon-to-nitrogen (C:N) ratio - the proportion of carbon to nitrogen in its dry matter. This calculator estimates the combined ratio of your pile as a weight-weighted average of the two materials' typical ratios:

Combined C:N = (Browns weight × Browns C:N + Greens weight × Greens C:N) ÷ (Browns weight + Greens weight)

For example, 10 lbs of dry leaves (~60:1) mixed with 10 lbs of grass clippings (~20:1) gives (10×60 + 10×20) ÷ 20 = 40:1. This is a practical estimate using typical published ratios for common materials, not a laboratory assay of your exact pile - real materials vary with moisture, age, and source.

Understanding the inputs

Browns are dry, carbon-rich materials - fallen leaves, straw, cardboard, wood chips. Greens are moist, nitrogen-rich materials - grass clippings, vegetable scraps, coffee grounds, manure. Weigh each material (a kitchen or bathroom scale works fine) and enter the weight in pounds; the calculator uses your selected material's typical C:N ratio to do the rest.

Interpreting the results

The Combined C:N Ratio is the headline number - compare it to the ideal 25-30:1 range shown in the indicator below the results. Total Mix Weight and Browns Share describe the composition of what you entered. Suggested Adjustment estimates roughly how many pounds of browns or greens to add to bring the ratio toward the midpoint of the ideal range (about 27.5:1); if your mix is already balanced, it will say so.

Frequently Asked Questions

What is the ideal carbon-to-nitrogen (C:N) ratio for compost?
Most composting guides recommend a C:N ratio of about 25:1 to 30:1 by weight for fast, low-odor decomposition. Below that range the pile tends to run wet and smell of ammonia; above it, microbes run short on nitrogen and breakdown slows dramatically.
How does this calculator estimate my mix's C:N ratio?
It multiplies the weight of your chosen brown (carbon-rich) material and green (nitrogen-rich) material by each material's typical published C:N ratio, adds the two totals, and divides by your total weight - a weight-weighted average. It is a practical estimate based on typical published values, not a lab assay of your specific materials.
What counts as a brown versus a green?
Browns are dry, carbon-rich materials such as fallen leaves, straw, cardboard, and wood chips. Greens are moist, nitrogen-rich materials such as grass clippings, vegetable scraps, coffee grounds, and manure. The names describe typical color and moisture, not a strict rule.
My ratio came out too high or too low - what should I do?
If the ratio is above 30:1 (too carbon-rich), mix in more greens to add nitrogen and moisture. If it is below 25:1 (too nitrogen-rich), add more browns to absorb excess moisture and reduce odor. The Suggested Adjustment result estimates roughly how many pounds to add.