TryBuildCalcHow Much Brown and Green Material for Compost? (Compost Recipe Calculator)
Find your exact brown/green mix instantly.
🕒 Last updated: September 22, 2026
Inputs
ℹ️Total volume of the finished, mixed pile or bin you're filling. A roughly 3 ft x 3 ft x 3 ft bin/pile (27 cu ft / 1 cu yd) is the commonly-cited minimum size to self-insulate and reach hot composting temperatures.
Target C:N Ratio
ℹ️The commonly-recommended range for active, hot composting is roughly 25:1-30:1 (Cornell Waste Management Institute cites ~30:1 as the ideal). A lower ratio composts faster but risks losing nitrogen as ammonia odor; a higher ratio decomposes more slowly.
Brown Material (Carbon)
ℹ️Carbon-rich, dry/woody material — the ingredient that balances a nitrogen-rich green.
Cornell's On-Farm Composting Handbook table gives straw a typical C:N ratio of 80:1 (range 48-150:1) and 0.7% nitrogen (dry weight) at 12% moisture. Bulk density is not in Cornell's own table — this preset's ~7 lb/cu ft loose figure is cross-checked against independent agricultural bulk-density references for loose (unbaled) straw.
Green Material (Nitrogen)
ℹ️Nitrogen-rich, moist material — the ingredient that balances a carbon-rich brown.
C:N ratio (19:1), %nitrogen (2.7%, dry weight), and moisture (87%) are Cornell's own On-Farm Composting Handbook figures for "vegetable produce" — broadly consistent with Cornell's separate chapter citing 10-20:1 for vegetable scraps and 20-50:1 for fruit wastes generally. Bulk density is this preset's lowest-confidence figure: Cornell's own table lists a very dense ~1,585 lb/cu yd for compacted wet processing waste, which is unrepresentative of loosely piled diced kitchen scraps — this preset instead uses an estimated ~45 lb/cu ft (moist, loosely piled), cross-checked against general compost-weight references rather than a single extension-sourced figure.
Cost (Optional)
Brown Material Needed
22.31
cu ft (0.826 cu yd) — 156.2 lb (70.8 kg)
Green Material Needed
27.69
cu ft (1.026 cu yd) — 1245.9 lb (565.1 kg)
Target C:N ratio 30:1 achieved (as mixed: 30:1) for a 50 cu ft (1.852 cu yd) pile
Mixture moisture (as mixed): 78.6% by weight
This blend works out to about 79% moisture by weight — above the commonly-recommended 40-60% range (Cornell: a pile should feel like a wrung-out sponge). Above roughly 60%, water crowds out the air pockets a pile needs and it becomes prone to compacting and going anaerobic (slow, smelly decomposition) — regardless of how close the C:N ratio is to the target. Mix in more dry brown material, or turn the pile more often to help it dry out.
Brown Material (Carbon)
Material: Straw
C:N ratio: 80:1
Volume: 22.31 cu ft (0.632 m³)
Weight: 156.2 lb (70.8 kg)
Green Material (Nitrogen)
Material: Vegetable & Fruit Scraps
C:N ratio: 19:1
Volume: 27.69 cu ft (0.784 m³)
Weight: 1245.9 lb (565.1 kg)
Estimated Finished Compost Yield
Roughly 15-25 cu ft (0.556-0.926 cu yd) once fully broken down and settled.
A rough estimate only — composting typically reduces starting volume by roughly 50-70% as organic matter breaks down, moisture evaporates, and the pile settles, but real shrinkage varies hugely by materials, moisture, turning frequency, and climate. Do not treat this as a precise figure.
Assumptions Used
This calculator blends the brown and green materials by MASS (weight), not by volume — a physically correct C:N ratio depends on the actual carbon and nitrogen MASS in the mix, and materials like dry leaves and wet food scraps differ enormously in weight per cubic foot. Straw is used at 80:1 C:N, 0.7% nitrogen (dry weight), 12% moisture, and 7 lb/cu ft bulk density; Vegetable & Fruit Scraps is used at 19:1 C:N, 2.7% nitrogen (dry weight), 87% moisture, and 45 lb/cu ft bulk density. Cornell's On-Farm Composting Handbook table gives straw a typical C:N ratio of 80:1 (range 48-150:1) and 0.7% nitrogen (dry weight) at 12% moisture. Bulk density is not in Cornell's own table — this preset's ~7 lb/cu ft loose figure is cross-checked against independent agricultural bulk-density references for loose (unbaled) straw. C:N ratio (19:1), %nitrogen (2.7%, dry weight), and moisture (87%) are Cornell's own On-Farm Composting Handbook figures for "vegetable produce" — broadly consistent with Cornell's separate chapter citing 10-20:1 for vegetable scraps and 20-50:1 for fruit wastes generally. Bulk density is this preset's lowest-confidence figure: Cornell's own table lists a very dense ~1,585 lb/cu yd for compacted wet processing waste, which is unrepresentative of loosely piled diced kitchen scraps — this preset instead uses an estimated ~45 lb/cu ft (moist, loosely piled), cross-checked against general compost-weight references rather than a single extension-sourced figure. This calculator estimates a recipe split and finished-yield range only — it does not manage moisture, turning/aeration, or pile temperature, all of which also matter for successful composting.
Diagram simplified for clarity (not to scale) — pile shown schematically, layer heights reflect the real brown:green volume split.
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Compost Calculator.
The right brown:green mix for your specific materials
There's no single fixed brown:green ratio that works for every material — a common rule of thumb cites roughly 2-3 volumes of browns to 1 volume of greens, but the exact right split depends heavily on which specific materials you're using, since C:N ratio, %nitrogen, and bulk density all vary meaningfully by material.
This page defaults to a 50 cu ft pile of straw and vegetable/fruit scraps targeting a 30:1 ratio — edit the inputs above to match your own pile size and the specific materials you actually have on hand.
Compost Calculator Formula: How Is It Determined?
A target pile volume, a target C:N ratio, and each material's own C:N ratio/%nitrogen/bulk density/moisture combine into a real mass-weighted blend — never a rough volume-only split.
Step 1 — Pile/Bin Volume
By Total Volume: Volume = entered value
By Bin Dimensions: Volume = Length x Width x Height
Either enter the target total volume directly, or enter a rectangular bin's length, width, and height.
Step 2 — Nitrogen Mass per Unit Volume
Nitrogen per cu ft = Bulk Density x (%Nitrogen / 100) x (1 - Moisture% / 100)
%Nitrogen is measured on a DRY-WEIGHT basis, so it only applies to the material's dry portion — bulk density (the material's as-piled weight per cu ft) times (1 - moisture%) gives the dry weight per cu ft, which is then multiplied by %nitrogen to get actual nitrogen mass per cu ft. This is the building block the whole blend depends on — see the Reference Tables section below for why skipping this step (mixing by volume alone) gives a physically wrong C:N ratio.
Step 3 — Volume Split to Hit the Target Ratio
Brown Volume = Total Volume x [Green N/cu ft x (Target - Green Ratio)] / Denominator
Denominator = Brown N/cu ft x (Brown Ratio - Target) + Green N/cu ft x (Target - Green Ratio)
Green Volume = Total Volume - Brown Volume
Derived from the identity that a blend's overall C:N ratio is the NITROGEN-MASS-weighted average of each material's own ratio (R = total Carbon mass / total Nitrogen mass, and each material's own Carbon mass = Nitrogen mass x that material's own C:N ratio). This engine's formula was independently re-derived and verified against Cornell Waste Management Institute's own published worked example (a real 10 kg grass + leaves mix targeting 30:1) — see the Reference Tables section for the comparison.
Step 4 — Weight
Material Weight = Material Volume x Material Bulk Density
Each material's resulting volume converts directly to weight using its own bulk density, so you can weigh out ingredients instead of (or in addition to) measuring volume.
Step 5 — Estimated Finished Yield
Low Estimate = Total Volume x 30% (i.e. 70% shrinkage)
High Estimate = Total Volume x 50% (i.e. 50% shrinkage)
Composting typically reduces starting volume by roughly 50-70% as organic matter breaks down, moisture evaporates, and the pile settles — shown as a RANGE with an explicit caveat, since real shrinkage varies hugely by materials, moisture, turning frequency, and climate.
Worked Example
This example walks through your current inputs above, using the same steps as the Formula section.
Input Values Used
| Input | Value | Why it is used |
|---|---|---|
| Total Volume | 50 cu ft (1.852 cu yd) | Sets the total to split between materials |
| Target C:N Ratio | 30:1 | Sets the blend goal |
| Brown Material | Straw (80:1, 0.7%N, 7 lb/cu ft, 12% moisture) | Carbon side of the blend |
| Green Material | Vegetable & Fruit Scraps (19:1, 2.7%N, 45 lb/cu ft, 87% moisture) | Nitrogen side of the blend |
Step 1-3 — Volume Split
| Calculation | Result |
|---|---|
| Brown Volume (mass-weighted split, solved for target 30:1) | 22.31 cu ft |
| Green Volume = 50 - 22.31 | 27.69 cu ft |
| As-Mixed C:N Ratio (independent check) | 30:1 |
| As-Mixed Moisture (weight-weighted blend) | 78.6% |
Step 4 — Weight
| Calculation | Result |
|---|---|
| Brown Weight = 22.31 cu ft x 7 lb/cu ft | 156.2 lb (70.8 kg) |
| Green Weight = 27.69 cu ft x 45 lb/cu ft | 1245.9 lb (565.1 kg) |
Step 5 — Estimated Finished Yield
| Calculation | Result |
|---|---|
| Low Estimate = 50 cu ft x 30% | 15 cu ft |
| High Estimate = 50 cu ft x 50% | 25 cu ft |
Figures above are rounded for display; the real recipe split is always calculated from full, unrounded values, so it can occasionally look off by a hair if you redo the division yourself using the rounded figures shown.
Therefore, a 50 cu ft pile targeting 30:1 needs approximately 22.31 cu ft (156.2 lb) of Straw and 27.69 cu ft (1245.9 lb) of Vegetable & Fruit Scraps.
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Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.