Compost Carbon-to-Nitrogen (C:N) Ratio Calculator

Compost Mix Check

{{ `${formatNumber(summary.finalRatio || 0, 1)} : 1` }}

Target {{ targetRangeLabel }} • Moisture {{ moistureRangeLabel }} • Dry basis mode

Measurement system:

Target ratio minimum:

: 1

Target ratio maximum:

: 1

Account for moisture:

Materials

Start with balanced mix: browns such as leaves or straw deliver carbon, greens like food scraps and manure deliver nitrogen. Ratio and moisture values are editable.

Add your first material to start calculating the blend.

Material {{ index + 1 }}

Preset:

Name:

C:N ratio:

: 1

Moisture:

Water is removed before blending so ratios reflect dry matter.

Weight:

{{ weightUnitLabel }}:

Target preset:

Moisture target minimum:

Moisture target maximum:

Brown repair helper:

Green repair helper:

Metric	Value	Copy
{{ row.label }}	{{ row.value }}

{{ line }}

Target	Helper	Wet add	Dry add	Projected ratio	Projected moisture	Note
{{ row.label }}	{{ row.helperLabel }}	{{ row.wetWeightDisplay }}	{{ row.dryWeightDisplay }}	{{ row.projectedRatioDisplay }}	{{ row.projectedMoistureDisplay }} {{ row.projectedMoistureStatus }}	{{ row.note }}

Material	C:N	Wet weight	Dry weight	Water	Carbon	Nitrogen	Copy
{{ row.label }} {{ row.materialClass }} • {{ formatPercent(row.moisturePercent, 0) }} moisture • Dry basis	{{ row.ratioDisplay }}	{{ row.wetWeightDisplay }}	{{ row.dryWeightDisplay }}	{{ row.waterDisplay }}	{{ row.carbonDisplay }}	{{ row.nitrogenDisplay }}

Add at least one material to chart dry mass distribution.

Add at least one material to chart carbon and nitrogen contributions.

Add materials to generate the mass components chart.

Add your brown and green ingredients to see the blended C:N ratio, moisture window, and repair guidance for balancing the pile.

Tags: Education , Gardening

Export to PDF Fullscreen

Include query parameters

Embed:

Customize embed code

Include query parameters

Wrap embed in collapsible toggle

Collapse panel by default

Hide card frame (bare iframe)

Loading behavior

Width

Height

Aspect ratio (width : height)

Max height (optional)

Collapsible heading

Collapsible description (optional)

Allow fullscreen

Referrer policy

Sandbox tokens

Compost microbes need carbon as an energy source and nitrogen to build proteins and reproduce. When those inputs are badly out of balance, a pile can turn slimy, smelly, slow, or disappointingly cool even when it looks full of useful material.

This calculator turns that biology into a mix-planning estimate. You load materials with a carbon-to-nitrogen ratio, a moisture estimate, and a weight, and it returns a blended ratio, a target-band classification, practical balancing guidance, contributor summaries, three chart views, and exports for the finished scenario.

That is most helpful when you already have a real pile or recipe in mind and want to know whether it is brown-heavy, green-heavy, or sitting near a workable hot-compost window. A bucket of kitchen scraps, a pile of fresh grass, and a bag of dry leaves do not contribute equally just because they weigh the same when wet. Moisture and carbon density change the picture quickly.

The calculator is also built for adjustment rather than blind trust. It offers presets for common ingredients such as dry leaves, grass clippings, kitchen scraps, coffee grounds, straw, wood-heavy materials, manures, alfalfa, and shredded cardboard, but every ratio and moisture value remains editable because real compost feedstocks vary with age, storage, and local conditions.

One boundary matters from the start. Landing inside the target band does not guarantee a perfect pile. Aeration, pile size, texture, temperature, and moisture management still matter. The result is a strong planning aid for mix balance, not a complete compost-performance simulator.

Everyday Use & Decision Guide:

For a first run, leave the default target band at 25:1 to 35:1 and keep Account for moisture enabled unless the weights you are entering are already dry-matter measurements. Then add the materials you actually have on hand before worrying about fine tuning the last decimal place.

Use the presets as a starting point, not as a fixed scientific truth. If your leaves are wetter than usual or your bedding is much woodier than the preset, edit the values before trusting the blend.
Read the summary box first. It shows the final ratio, whether the mix is Balanced, Nitrogen heavy, or Carbon heavy, and the immediate guidance line for what to add next.
The summary table is more than a verdict. It also calls out wet mass, dry mass, total carbon, total nitrogen, moisture loss, the largest dry-matter contributor, the largest nitrogen contributor, and any calculated rebalance action.
If the mix misses the target band, the calculator tries to steer it toward the midpoint of the band with a concrete helper-material suggestion instead of a generic “add more browns” or “add more greens” statement.

The different tabs support different questions. Materials is the audit trail for each ingredient, Dry Mass Distribution shows which ingredient dominates the solids, Carbon & Nitrogen compares nutrient contribution by material, Mass Components breaks the mix into carbon, nitrogen, removed moisture, and residual dry matter, and JSON keeps a structured record of the run.

Technical Details:

The calculator converts each ingredient to an internal kilogram basis, optionally removes water, and then splits the remaining dry matter into carbon and nitrogen shares using the entered ratio. That matters because compost ratios are about dry matter, not fresh weight. A soggy bucket of scraps can look large by weight while contributing far less dry carbon or dry nitrogen than its wet mass suggests.

For each material, the ratio is interpreted as parts carbon to one part nitrogen. Once dry mass is known, carbon is calculated as ratio divided by ratio plus one, and nitrogen is the remaining one part. The blended ratio is then total carbon divided by total nitrogen across the whole mix.

Formula Core:

\begin{matrix} M_{d, i} & = & M_{w, i} \times (1 - m_{i}) \\ C_{i} & = & M_{d, i} \times \frac{R_{i}}{R_{i} + 1} \\ N_{i} & = & M_{d, i} \times \frac{1}{R_{i} + 1} \\ R_{mix} & = & \frac{\sum C_{i}}{\sum N_{i}} \end{matrix}

Compost ratio symbols
Symbol	Meaning in this calculator	Source
`M_w,i`	Wet mass of one ingredient	Weight
`m_i`	Moisture fraction for that ingredient	Moisture
`R_i`	Ingredient carbon-to-nitrogen ratio	C:N ratio
`M_d,i`	Dry mass after removing water	Derived
`C_i`	Carbon share of the dry mass	Derived
`N_i`	Nitrogen share of the dry mass	Derived
`R_mix`	Final blended ratio for the whole recipe	Derived

Classification is straightforward. A result below the lower bound is marked Nitrogen heavy, a result above the upper bound is Carbon heavy, and a result inside the band is Balanced. The default band is 25:1 to 35:1, but the range is user-defined because different composting goals and materials justify different targets.

The midpoint of the target band also drives the rebalancing helper. If the mix is too nitrogen-heavy, the calculator estimates how much Dry leaves would need to be added to reach the midpoint. If the mix is too carbon-heavy, it uses Fresh grass clippings as the helper material. The suggestion is expressed as both wet and dry weight so you can plan with the material as handled and still understand the dry-matter effect.

Primary outputs in the compost ratio calculator
Output	What it tells you
Summary	Final ratio, classification, guidance, total wet and dry mass, moisture loss, dominant contributors, and any rebalance action.
Materials	Per-material wet weight, dry weight, carbon, nitrogen, and the exact ratio used in the calculation.
Dry Mass Distribution	A donut view of which ingredients dominate the solids in the pile.
Carbon & Nitrogen	A stacked bar comparison of absolute carbon and nitrogen contribution by material.
Mass Components	A composition view of carbon, nitrogen, removed moisture, and any remaining dry matter not counted as those two fractions.
JSON	A structured export of the inputs, summary, and per-material breakdown.

All calculations stay in the browser. Unit switching converts existing material weights between pounds and kilograms, and the export actions generate local CSV, DOCX, chart-image, or JSON files without server-side processing.

Step-by-Step Guide:

Choose the Measurement system you want to work in, then confirm the target band. The default 25:1 to 35:1 range is a reasonable starting point for active composting.
Decide whether Account for moisture should stay on. Leave it on for fresh materials weighed as collected, and switch it off only when your weights already reflect dry matter.
Add materials one by one. Start from a preset when it matches what you have, then edit the name, ratio, moisture, or weight if your real feedstock differs.
Read the summary card before anything else. It tells you whether the mix is in range and whether the next move is to add more carbon-rich or nitrogen-rich material.
Use Materials to audit each ingredient and the charts to see dominance, nutrient contribution, and moisture removal visually.
If the recipe looks good, export the summary, charts, or JSON so the mix can be repeated or compared with a revised batch later.

Interpreting Results:

Balanced means the blended ratio lands inside your chosen band. It does not guarantee ideal airflow, temperature, or moisture management.
Moisture loss tells you how much of the loaded mass was treated as water and removed before the carbon and nitrogen math. A high percentage means fresh weight was hiding a smaller dry-matter contribution.
Largest dry matter share and Largest nitrogen share can point to different materials. A bulky brown may dominate solids, while a smaller green can still dominate nitrogen.
The Mass Components chart includes Other dry matter when dry mass remains after carbon and nitrogen fractions are separated. That keeps the composition view honest instead of pretending the whole dry mix is only carbon plus nitrogen.
The rebalance line is a planning estimate toward the midpoint of your band, not a mandatory correction. Many composters intentionally stay slightly brown-heavy to control odor and wetness.

Worked Examples:

A mixed pile that lands inside the default band

Enter 20 lb of dry leaves at 60:1 and 10% moisture, 12 lb of kitchen scraps at 15:1 and 70% moisture, and 12 lb of fresh grass clippings at 17:1 and 70% moisture. The calculator returns a final ratio of about 34.0:1, which sits inside the default 25:1 to 35:1 band.

The same run shows 44.0 lb of wet mass but only 25.2 lb of dry mass, with about 42.7% moisture loss. In other words, nearly half the loaded weight was water, and the dry leaves dominate both dry matter and carbon contribution.

A greens-heavy mix that needs a carbon correction

Enter 20 lb of food scraps at 15:1 and 70% moisture plus 15 lb of fresh grass clippings at 17:1 and 70% moisture. The result is about 15.8:1, which the calculator marks as Nitrogen heavy.

The rebalance helper then suggests adding about 20.1 lb of dry leaves, equivalent to roughly 18.0 lb of dry matter, to steer the mix toward the midpoint near 30:1. That is a concrete example of why wet green mass can overpower a pile faster than it first appears.

FAQ:

Should I leave moisture accounting enabled?

Yes when the weights are fresh, as-collected materials. Turn it off only when you are deliberately entering dry weights or you have already corrected the material weights for moisture outside the calculator.

Are the preset ratios fixed scientific constants?

No. They are practical starting values. Real leaves, manures, bedding, and food scraps vary by source, age, and storage, which is why every preset stays editable.

Why did the result change when I switched units?

The calculator converts the existing ingredient weights between pounds and kilograms so the same recipe stays intact. Small rounding differences can appear because converted values are rounded for display and storage.

Does an in-range result guarantee a hot compost pile?

No. An in-range C:N ratio is helpful, but aeration, particle size, pile volume, and water management still control whether the pile actually heats and decomposes well.

Glossary:

Browns: Higher-carbon materials such as dry leaves, straw, cardboard, and woody feedstocks that usually raise the ratio.
Greens: Lower-ratio materials such as fresh grass, food scraps, and manures that usually raise nitrogen contribution.
Dry mass: The weight remaining after the calculator removes water from a material.
Moisture loss: The portion of the loaded weight treated as water rather than dry compost feedstock.
Target band: The acceptable ratio window chosen for the mix. The calculator uses this range for classification and midpoint rebalancing.