Compost Mix Ratio Calculator
Enter your ingredients and their ratio parts to get exact amounts for any batch size. Perfect for garden compost, potting mixes, and custom blends.
📦 Batch Settings
Enter the total volume or weight you want to make.
e.g., 2 = double batch, 0.5 = half batch.
🧪 Ingredients & Ratio
The sum of all ratio parts. Each ingredient's amount is calculated as: (part ÷ total parts) × batch size.
📊 Results
Total batch
100 L
Total parts
4
Ingredients
4
Important: Ratio mathematics vs. agronomic advice
This calculator handles the mathematics of ratios and scaling — it does not determine the "correct" recipe for your specific plants, climate, or materials. A 2:1:1 ratio is a common starting point, but the ideal mix depends on your ingredients' carbon-to-nitrogen (C:N) ratio, moisture, aeration, and intended use. Always test small batches and adjust based on local conditions and expert guidance.
Understanding compost mix ratios
A compost mix ratio is simply a proportional recipe. For example, a "2:1:1" ratio means 2 parts of ingredient A, 1 part of ingredient B, and 1 part of ingredient C. The total parts is the sum (2+1+1 = 4), and each ingredient's share is its part divided by the total. This calculator lets you define any number of ingredients and any ratio you like — then scales the amounts to your desired batch size.
Carbon-to-nitrogen (C:N) balance — general information
In composting, the carbon-to-nitrogen ratio is a common guideline. "Browns" (dry leaves, straw, cardboard) are high in carbon; "greens" (grass clippings, food scraps, coffee grounds) are high in nitrogen. A widely cited target is roughly 25:1 to 30:1 C:N by weight, but this varies enormously by material and composting method. This tool does not calculate C:N — it calculates the proportions you specify. If you want to hit a specific C:N, you would need to know the C:N of each ingredient and solve a different equation.
Moisture and aeration
The ideal moisture for active composting is often described as "wrung-out sponge" — about 40–60% moisture by weight. Aeration is equally important: turn or mix your pile regularly to supply oxygen. The ratio of ingredients affects both: overly wet, dense mixes can go anaerobic; overly dry mixes slow decomposition. Adjust by adding dry browns or water as needed — again, these are practical judgements, not mathematical outputs.
Ingredient variability
Every batch of leaves, grass, or kitchen scraps differs in nutrient content, particle size, and moisture. A ratio that works perfectly in summer may behave differently in winter. Treat any calculator (including this one) as a starting point, not a guarantee. Keep notes on what works in your garden.
Practical mixing considerations
- Chop or shred large materials to speed up decomposition.
- Mix thoroughly — layered "lasagna" composting works, but blending accelerates the process.
- Start with a batch size you can turn comfortably.
- If it smells bad, add more browns and turn it.
- Use the scaling feature to adjust recipes for small bins or large garden beds.
Frequently asked questions
What does "ratio parts" mean in this calculator?
"Parts" are relative proportions. If you enter 2, 1, and 1 for three ingredients, the total parts = 4. Ingredient 1 gets 2/4 (50%) of the batch, and ingredients 2 and 3 each get 1/4 (25%). You can use any numbers — they don't have to sum to 100.
Is a 2:1:1 compost mix always the best?
No. There is no single universal compost recipe. 2:1:1 is a common starting point for some gardeners, but the ideal mix depends on your materials, climate, and what you're growing. This tool lets you calculate any ratio you choose — it doesn't prescribe one.
Can I use weight instead of volume?
Yes — choose kilograms, pounds, or any weight unit from the dropdown. Just be consistent: if you enter your batch size in kg, the results will be in kg for each ingredient. Weight-based ratios are often more accurate for dense materials.
How do I scale a recipe up or down?
Two ways: change the "Total batch size" field, or use the "Scaling multiplier". For example, set batch to 100 L with multiplier 1, then change multiplier to 2 to get a 200 L batch. The ratio stays the same; only the total amount changes.
Does this calculator account for carbon-to-nitrogen ratio?
No. This tool only calculates proportions and scaling. C:N ratio requires knowing the carbon and nitrogen content of each ingredient — that's a separate calculation. We cover C:N at a general level in the guide above, but always verify with reliable local resources.
What if my compost pile smells or isn't heating up?
Smell usually means too much moisture or not enough oxygen — add dry browns and turn the pile. If it's not heating, it may need more nitrogen (greens), more moisture, or a larger pile. These are practical adjustments, not mathematical ones.
Can I save or share my results?
You can take a screenshot, print the page, or copy the numbers manually. We don't store your data — everything runs in your browser.
Are the results in the same unit as my batch size?
Yes. If you select "Liters" for batch size, every ingredient amount is shown in liters. If you select "kg", results are in kg. The percentages are unit-independent.
Related tools
Raised Garden Bed Soil Calculator
Estimate soil volume for raised beds.
Open tool →Mulch Bag Coverage Calculator
How many bags of mulch do you need?
Open tool →Potting Soil Volume Calculator
Calculate soil for pots and containers.
Open tool →Compost Mix Ratio Calculator
You're here!
Current toolLawn Seed Coverage Calculator
Seed your lawn with confidence.
Open tool →Plant Fertilizer Dilution Calculator
Mix fertilizer at the right strength.
Open tool →