Fertilizer & Compost
Compost C:N Ratio Calculator: Balance Greens & Browns
Use this compost ratio calculator to estimate the carbon nitrogen balance of greens and browns. It works as a compost carbon nitrogen calculator, greens and browns compost calculator, compost C N ratio calculator, and simple compost mix calculator for home piles.
Estimated compost balance
Compost mix results
This mix is near a common compost target range. Keep moisture and airflow in balance too.
What is a good compost C:N ratio?
A common compost target is around 25:1 to 35:1, with 30:1 often used as a simple benchmark. A lower number usually means the mix is nitrogen-heavy or too green. A higher number usually means the mix is carbon-heavy or too brown. This is an estimate because natural materials vary by moisture, age, plant type, and particle size.
Greens vs browns table
| Material | Type | Typical C:N estimate |
|---|---|---|
| Grass clippings | Green | 17:1 |
| Vegetable scraps | Green | 15:1 |
| Coffee grounds | Green | 20:1 |
| Dry leaves | Brown | 60:1 |
| Straw | Brown | 80:1 |
| Cardboard | Brown | 350:1 |
| Sawdust | Brown | 400:1 |
| Wood chips | Brown | 500:1 |
Formula used
The calculator estimates total carbon divided by total nitrogen from each material's C:N ratio:
estimated carbon = amount x ratio / (ratio + 1)
estimated nitrogen = amount x 1 / (ratio + 1)
blended C:N = sum(estimated carbon) / sum(estimated nitrogen)
Amounts work best as comparable dry-weight parts. Volume-based inputs are still approximate because wet grass, dry leaves, shredded cardboard, and wood chips have very different densities.
Example compost mix
A simple starter mix might use 1 part grass clippings, 1 part vegetable scraps, and 2 parts dry leaves. That usually lands near a balanced range, depending on moisture and how fresh the materials are. If the pile smells sour, add dry browns. If it stays dry and unchanged, add greens and moisture.
Common mistakes
- Treating compost C:N estimates as exact lab values.
- Adding too many wet greens without dry browns for structure.
- Using large cardboard or wood pieces that break down slowly.
- Ignoring moisture and airflow, even when the ratio looks balanced.
- Mixing units casually when a more precise estimate is needed.
FAQ
Compost ratio calculator FAQ
What is a good compost C:N ratio?
Many home compost piles work well around 25:1 to 35:1, with 30:1 often used as a simple target.
What are greens in compost?
Greens are nitrogen-rich materials such as grass clippings, vegetable scraps, coffee grounds, and fresh plant trimmings.
What are browns in compost?
Browns are carbon-rich materials such as dry leaves, straw, cardboard, sawdust, and wood chips.
Is this compost carbon nitrogen calculator exact?
No. It is an estimate because natural materials vary by moisture, age, species, and texture.
What should I do if the mix is too green?
Add browns such as dry leaves, straw, shredded cardboard, or wood chips.
What should I do if the mix is too brown?
Add greens such as grass clippings, vegetable scraps, or coffee grounds, and check moisture.
Can I use custom materials?
Yes. Choose Custom material, then enter the name, type, approximate C:N ratio, amount, and unit.
Which unit should I use?
Dry-weight parts are best. Volume units can be useful for rough pile planning, but moisture and density can change the real C:N balance.