TryBuildCalcKitchen Scraps Compost Calculator (Vegetable & Fruit Scraps + Browns)
Balance your kitchen scraps 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.
Source disagreement disclosed: this preset uses 350:1, the figure most commonly cited by consumer composting guides for shredded cardboard. Cornell Waste Management Institute's own EMPIRICAL lab table shows measured values running meaningfully higher — corrugated cardboard at 563:1 and newsprint at 398-852:1 — so treat 350:1 as a conservative, commonly-quoted middle figure rather than a precise measured constant; shred finely and mix well regardless, since coarse cardboard/paper decomposes slowly at any of these ratios.
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
5.22
cu ft (0.193 cu yd) — 46.9 lb (21.3 kg)
Green Material Needed
9.78
cu ft (0.362 cu yd) — 440.3 lb (199.7 kg)
Target C:N ratio 28:1 achieved (as mixed: 28:1) for a 15 cu ft (0.556 cu yd) pile
Mixture moisture (as mixed): 79.4% by weight
This 15 cu ft pile is smaller than the roughly 27 cu ft (about 3 ft x 3 ft x 3 ft) commonly cited as the minimum self-insulating mass needed to reach hot/thermophilic composting temperatures — it will still compost, just more slowly as a "cold pile," and won't reliably kill weed seeds or pathogens the way a hot pile can.
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: Cardboard / Newspaper (shredded)
C:N ratio: 350:1
Volume: 5.22 cu ft (0.148 m³)
Weight: 46.9 lb (21.3 kg)
Green Material (Nitrogen)
Material: Vegetable & Fruit Scraps
C:N ratio: 19:1
Volume: 9.78 cu ft (0.277 m³)
Weight: 440.3 lb (199.7 kg)
Estimated Finished Compost Yield
Roughly 4.5-7.5 cu ft (0.167-0.278 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. Cardboard / Newspaper (shredded) is used at 350:1 C:N, 0.1% nitrogen (dry weight), 8% moisture, and 9 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. Source disagreement disclosed: this preset uses 350:1, the figure most commonly cited by consumer composting guides for shredded cardboard. Cornell Waste Management Institute's own EMPIRICAL lab table shows measured values running meaningfully higher — corrugated cardboard at 563:1 and newsprint at 398-852:1 — so treat 350:1 as a conservative, commonly-quoted middle figure rather than a precise measured constant; shred finely and mix well regardless, since coarse cardboard/paper decomposes slowly at any of these ratios. 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.
Balancing wet, heavy kitchen scraps with dry browns
Vegetable and fruit scraps are very high in moisture (commonly 80-90%) and notably HEAVY per cubic foot compared to most browns — a bucket of kitchen scraps weighs far more than the same volume of dry leaves or shredded cardboard, which matters directly for the mass-weighted C:N math.
This page defaults to a 15 cu ft pile of shredded cardboard/newspaper and vegetable/fruit scraps targeting 28:1 — edit the inputs above to match your own pile size and preferred brown material. Always cover fresh food scraps with a layer of browns to help trap odors and avoid attracting pests.
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 | 15 cu ft (0.556 cu yd) | Sets the total to split between materials |
| Target C:N Ratio | 28:1 | Sets the blend goal |
| Brown Material | Cardboard / Newspaper (shredded) (350:1, 0.1%N, 9 lb/cu ft, 8% 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 28:1) | 5.22 cu ft |
| Green Volume = 15 - 5.22 | 9.78 cu ft |
| As-Mixed C:N Ratio (independent check) | 28:1 |
| As-Mixed Moisture (weight-weighted blend) | 79.4% |
Step 4 — Weight
| Calculation | Result |
|---|---|
| Brown Weight = 5.22 cu ft x 9 lb/cu ft | 46.9 lb (21.3 kg) |
| Green Weight = 9.78 cu ft x 45 lb/cu ft | 440.3 lb (199.7 kg) |
Step 5 — Estimated Finished Yield
| Calculation | Result |
|---|---|
| Low Estimate = 15 cu ft x 30% | 4.5 cu ft |
| High Estimate = 15 cu ft x 50% | 7.5 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 15 cu ft pile targeting 28:1 needs approximately 5.22 cu ft (46.9 lb) of Cardboard / Newspaper (shredded) and 9.78 cu ft (440.3 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.