Compost Calculator
Achieve rapid, odor-free hot composting by balancing your pile’s Carbon-to-Nitrogen (C:N) ratio. Calculate the perfect harmony between nitrogen-rich "greens" (kitchen scraps, fresh grass) and carbon-rich "browns" (dry leaves, cardboard, straw) to reach the ideal 25:1 to 35:1 decomposition threshold.
Weight of green materials (kitchen vegetable scraps, coffee grounds, fresh lawn clippings)
Typical internal carbon-to-nitrogen ratio of your green input
Weight of brown materials (autumn dry leaves, shredded cardboard, wood shavings, straw)
Typical internal carbon-to-nitrogen ratio of your brown input
Combined carbon-to-nitrogen ratio (target is 25:1 to 35:1)
How to Use This Calculator
- Estimate or weigh the pounds of green kitchen scraps or fresh grass you have.
- Select the closest category for your green input.
- Enter the weight of dry leaves, straw, or shredded cardboard added.
- Review the blended C:N ratio and follow the adjustment suggestions.
Formula & Calculation Methodology
Composting microorganisms require 30 parts of carbon (for cellular respiration and heat energy) for every 1 part of nitrogen (for protein synthesis and reproduction).
Worked Example
20 lbs kitchen scraps (17:1) mixed with 40 lbs dry leaves (60:1)
20 lbs kitchen scraps (17:1) mixed with 20 lbs dry leaves (60:1)
Frequently Asked Questions
Why is a 30:1 C:N ratio considered the golden rule of composting?↓
At roughly 30 parts carbon to 1 part nitrogen, thermophilic aerobic bacteria thrive, heating the pile core to 135°F–160°F (57°C–71°C) to kill weed seeds and pathogens without producing foul anaerobic sulfur or ammonia odors.
Why does my compost pile smell like rotten eggs or ammonia?↓
A foul odor indicates an excess of nitrogen (C:N ratio below 20:1) and too much moisture, which chokes out oxygen and creates anaerobic rot. Add dry shredded leaves, wood chips, or shredded cardboard and turn the pile to aerate.
Are coffee grounds considered a green or a brown?↓
Despite their brown color, spent coffee grounds are chemically a "green" with a rich C:N ratio of around 20:1, making them a great nitrogen booster for compost heaps.
What is a limitation of compost recipe calculators?↓
Moisture level (optimal at 40%–60%, feeling like a wrung-out sponge) and particle size (shredding materials accelerates surface area contact) are equally vital physical factors alongside chemical C:N math.
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Source Citation & Disclaimer
Informational tool only; not licensed tax, legal, or financial advice.