Compost Tea Ratio Calculator
Compost tea is brewed by steeping compost in water at a chosen ratio, then often diluted further before watering. For a given tank size, the compost fraction is one over (one plus the water-to-compost ratio) and the rest is water. This calculator splits your tank into compost and water by the ratio you set, then applies a dilution factor to show the final volume you can apply. Brew ratios are recipe choices that vary widely rather than a fixed standard, so they are user inputs. The arithmetic is exact proportioning.
Compost tea formula
Compost fraction = 1 / (1 + ratio)
Compost = tank * compost fraction
Water = tank - compost
Final volume = tank * dilution factor
Dilution water to add = final volume - tank
The ratio is water parts per one part compost, so a ratio of 8 means 1 part compost to 8 parts water. The dilution factor multiplies the finished brew volume; a factor of 1 means no dilution.
Compost tea context
- Compost tea steeps finished compost in water to extract soluble nutrients and microbes.
- Brew ratios are recipe choices and vary widely; there is no single official figure.
- Diluting the finished brew is common, especially for seedlings, to avoid over-feeding.
- Certified organic operations follow USDA National Organic Program rules for compost.
- Follow local guidance for handling compost products near edible crops and waterways.
Compost tea: frequently asked questions
What is compost tea?
Compost tea is a liquid made by steeping finished compost in water, often aerated, to extract soluble nutrients and microbes for watering plants or as a foliar spray. The strength is set by the ratio of compost to water you brew, then it is often diluted further before applying.
What ratio of compost to water should I use?
Common home recipes use roughly 1 part compost to 5 to 10 parts water by volume for the brew, but there is no single official figure, and recipes vary widely. Because it is a recipe choice rather than a fixed standard, this calculator takes your ratio as an input so you can match the method you are following.
How is the brew split between compost and water?
For a given tank size, the compost fraction is 1 divided by (1 plus the water-to-compost ratio), and the water fraction is the rest. Multiply each fraction by the tank volume to get the compost and water amounts. This calculator does that and also shows the diluted volume you can apply.
Should I dilute compost tea before using it?
Many gardeners dilute the finished brew with plain water before applying, especially for seedlings, to avoid over-feeding. Enter a dilution factor (for example 2 means one part tea to one part water, doubling the volume). The calculator reports the final volume you can apply after dilution.
Is compost tea regulated?
Composting and soil amendments are addressed by the EPA and USDA, and certified organic operations follow USDA National Organic Program rules on compost and any teas made from it. Always follow local guidance for handling and applying compost products, particularly near edible crops and waterways.
Official sources
- U.S. Environmental Protection Agency: EPA Composting.
- U.S. Department of Agriculture: USDA Agricultural Marketing Service (National Organic Program).
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.