Compost Calculator
Green Materials (Nitrogen-Rich)
Brown Materials (Carbon-Rich)
C:N Ratios for Common Compost Materials
Green materials (nitrogen) and brown materials (carbon)
| Material | Type | C:N Ratio | Notes |
|---|---|---|---|
| Coffee grounds | Green | 7:1 | Excellent nitrogen source |
| Fresh manure | Green | 12:1 | Chicken highest, horse lower |
| Food scraps | Green | 15:1 | Fruit/veggie scraps |
| Grass clippings | Green | 20:1 | Fresh, not dried |
| Dry leaves | Brown | 60:1 | Shred for faster breakdown |
| Straw | Brown | 80:1 | Not hay (hay has seeds) |
| Wood chips | Brown | 100:1 | Best for paths/mulch |
| Cardboard | Brown | 400:1 | Shred; remove tape/plastic |
| Sawdust | Brown | 500:1 | Use sparingly; compacts |
How We Calculate This
This compost calculator uses established formulas and industry-standard data to provide accurate estimates.
- Enter your specific values into the calculator fields above
- Our algorithm applies the relevant formulas using your inputs
- Results are calculated instantly in your browser — nothing is sent to a server
- Review the detailed breakdown to understand how each factor affects your result
These calculations are estimates based on standard formulas. For critical decisions, always consult a qualified professional.
How to Convert Oven Recipes to Air Fryer
Composting works best when the carbon-to-nitrogen (C:N) ratio is around 25:1 to 35:1, with 30:1 being the ideal target.
The basic rule:
- Target C:N ratio for active composting: 25:1 to 35:1 (ideal: 30:1)
- Green materials provide nitrogen (low C:N) — food scraps, grass, manure
- Brown materials provide carbon (high C:N) — leaves, straw, cardboard
- Blended C:N = (green_vol × green_CN + brown_vol × brown_CN) ÷ total_vol
- Too much nitrogen (low ratio): smelly, slimy pile. Add browns.
- Too much carbon (high ratio): slow decomposition. Add greens.
In practice, a volumetric ratio of roughly 3 parts brown to 1 part green by volume achieves close to the 30:1 C:N target for most common materials.
When Would You Use This Calculator?
This compost calculator is designed for anyone who needs quick, reliable estimates without complex spreadsheets or professional consultations.
- When you need a quick estimate before committing to a purchase or project
- When comparing different options or scenarios side by side
- When planning a budget and need to understand potential costs
- When you want to verify a quote or estimate you've received from a professional
- When teaching or learning about the concepts behind these calculations
Frequently Asked Questions
What is the ideal compost ratio?
The ideal carbon-to-nitrogen ratio is 25:1 to 35:1 by weight, with 30:1 as the sweet spot. By volume, this roughly translates to 3 parts brown materials to 1 part green materials, since browns are less dense.
My compost smells bad — what should I do?
Bad smell means too much nitrogen (greens) or not enough air. Add brown materials like dry leaves, straw, or shredded cardboard, and turn the pile to add oxygen. The smell should improve within a day or two.
My compost is not heating up — why?
Common causes: not enough nitrogen (add greens), pile is too small (needs 3×3×3 ft minimum), too dry (add water until damp like a wrung sponge), or needs turning for oxygen.
How long does composting take?
Hot composting with proper C:N ratio and regular turning: 4-8 weeks. Cold composting (pile and wait): 6-12 months. Vermicomposting (worm bin): 3-6 months. The C:N ratio significantly affects speed.