Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Blended C:N ratio
33.5
Browns needed for target (lb)
77
Browns to add (lb)
-23
Total pile weight (lb)
160
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter browns (carbon material) (lb).
- 2Enter browns c:n ratio.
- 3Enter greens (nitrogen material) (lb).
- 4Enter greens c:n ratio.
- 5Enter target c:n.
- 6Read your blended c:n ratio on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
A hot pile needs a carbon-to-nitrogen ratio near 30:1. Enter the volumes and C:N values of your two main materials to see the blended ratio and how to adjust it.
Worked example
Using the values the calculator loads with:
Inputs
- Browns (carbon material): 100 lb
- Browns C:N ratio: 100
- Greens (nitrogen material): 60 lb
- Greens C:N ratio: 15
- Target C:N: 30
Results
- Blended C:N ratio: 33.5
- Browns needed for target (lb): 77
- Browns to add (lb): -23
- Total pile weight (lb): 160
What each field means
Inputs
- Browns (carbon material) (lb)
- The browns (carbon material) used in the calculation, measured in lb. Starts at 100 lb so you have a working example on load.
- Browns C:N ratio
- The browns c:n ratio used in the calculation. Starts at 100 so you have a working example on load.
- Greens (nitrogen material) (lb)
- The greens (nitrogen material) used in the calculation, measured in lb. Starts at 60 lb so you have a working example on load.
- Greens C:N ratio
- The greens c:n ratio used in the calculation. Starts at 15 so you have a working example on load.
- Target C:N
- The target c:n used in the calculation. Starts at 30 so you have a working example on load. Accepted range: 15–40.
Results
- Blended C:N ratio
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Browns needed for target (lb)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Browns to add (lb)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total pile weight (lb)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
What happens outside 25–35:1?
Too much carbon and the pile stalls cold. Too much nitrogen and it goes anaerobic and smells like ammonia.
Typical C:N values?
Dry leaves 60:1, cardboard 350:1, straw 75:1, grass clippings 17:1, food scraps 15:1, manure 15–20:1.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Compost C:N Ratio Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/compost-mix-ratio
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/compost-mix-ratio" target="_blank" rel="noopener">Compost C:N Ratio Calculator — RevenueLab</a> (2026).</p>
Source: [Compost C:N Ratio Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/compost-mix-ratio) (2026).