Compost Carbon-to-Nitrogen Ratio Calculator

This calculator combines the quantities and typical carbon-to-nitrogen ratios of your brown and green ingredients, estimates the blended C:N ratio, and tells you whether it is within the commonly targeted 25:1 to 30:1 range. Add every material using one consistent quantity unit, such as kilograms, pounds, buckets, or wheelbarrow loads. The result includes a transparent contribution breakdown, making it easier to adjust a recipe before building or turning the pile.

Enter a consistent compost recipe

Separate the recipe into browns and greens, then add a row for each material. Browns are generally dry, carbon-rich inputs such as fallen leaves, shredded cardboard, straw, sawdust, or wood chips. Greens are generally fresher, nitrogen-rich inputs such as grass clippings, food scraps, coffee grounds, or manure. For each row, enter the amount and a typical C:N ratio from a source appropriate to that material. Every amount must use the same basis. You can use kilograms or pounds when weighing ingredients, or use buckets when measuring everything by volume, but do not mix a weight for one material with a volume for another and expect a precise result. A zero quantity is allowed when keeping a planned ingredient in the recipe, while a negative quantity is rejected because it has no physical meaning. Typical ratios are estimates: moisture, maturity, species, and storage conditions can change the actual composition. Treat the result as a practical planning estimate rather than a laboratory analysis of your exact feedstocks.

Understand the mass-balance calculation

The calculator does not take a simple weighted average of the C:N numbers. A ratio describes two constituent shares, so a material listed at 60:1 is treated as sixty carbon parts and one nitrogen part out of sixty-one total parts. Its estimated carbon fraction is therefore 60 divided by 61, and its nitrogen fraction is 1 divided by 61. Each fraction is multiplied by that material's quantity. The carbon contributions from all brown and green rows are added together, the nitrogen contributions are added separately, and total carbon is divided by total nitrogen to obtain the blended ratio. This mass-balance method correctly handles ingredients with very different ratios. The output reports carbon units, nitrogen units, the final ratio, and every row's contributions so the arithmetic can be inspected. Because the inputs are typical ratios rather than chemical measurements, the displayed precision is useful for repeatability but should not imply laboratory certainty. The group labels organize the recipe; both groups participate in exactly the same calculation.

Interpret and adjust the result

A blended result from 25:1 through 30:1, including both endpoints, is flagged as ideal. Below 25:1, the recipe is marked too nitrogen-rich. Such a pile may become dense, wet, odorous, or prone to ammonia loss, so adding a dry high-carbon brown can move the estimate upward while also improving structure. Above 30:1, the recipe is marked too carbon-rich. Decomposition may proceed slowly because microbes have relatively little nitrogen, so adding a suitable green can move the estimate downward. Make adjustments by changing realistic quantities and recalculating; do not change a material's typical ratio merely to force a desired answer. Ratio is only one part of successful composting. Moisture should resemble a wrung-out sponge, bulky particles should preserve airflow, and the pile needs enough volume and occasional turning to manage oxygen and heat. If the result looks ideal but the pile performs poorly, check those physical conditions and reconsider whether the typical ratios accurately represent the actual materials. The API costs $0.002 per request when you automate repeated recipe checks.