Basics and units
Volume at 20 °C (wort shrinkage)
You read 23 L at the end of the boil, but only 22 will go into the fermenter. Hot water takes up more room than cold water, and this tool makes the correction.
Result
Fill in the values and run the calculation, or try the example.
This is the calculation Krausi uses. Create an account to save it in a recipe or a brew.
Create my accountWhy bring a volume back to 20 °C?
A volume measured at 100 °C overstates the amount of beer: as it cools, the wort shrinks by about 4%. Of 23 L read in the kettle, almost a litre is missing once at fermentation temperature.
Without this correction, the original gravity looks higher than expected, the calculated efficiency is wrong and a few bottles are missing at the end. Correcting the volume lets you compare like with like: volumes at 20 °C.
You use it at the end of the boil, before chilling, and whenever you read a volume on a hot liquid.
How is the shrinkage calculated?
The volume at 20 °C follows from the density of water, which drops as the temperature rises:
V20 = V × ρ(T) / ρ(20)The density is interpolated between reference values: 999.84 kg/m³ at 0 °C, 998.20 at 20 °C, 992.20 at 40 °C, 983.20 at 60 °C, 971.80 at 80 °C and 958.36 at 100 °C.
The result also gives the shrinkage rate, the share of volume lost on returning to 20 °C.
Worked example
Values entered
- Measured volume in litres: 25
- Temperature of the liquid when measured, in °C: 80
Result from the tool
- Equivalent volume at 20 °C, in litres
- 24.34 L
- Shrinkage (V − V20) / V, in %
- 2.64 %
- Density of water interpolated at the given temperature
- 971.8
What the tool does not do
- The density is that of pure water, not of wort: in practice the gap is negligible.
- Temperatures range from 0 to 100 °C.
- The tool does not correct for the expansion of the vessel itself.
Frequently asked questions
Why does my volume drop as it cools?
Water expands when heated. At 100 °C, one litre of cold water takes up about 1.04 L. As it cools, the wort returns to its original volume: nothing is lost, it was the hot measurement that was inflated.
What shrinkage percentage between 100 and 20 °C?
About 4%: 23 L at 100 °C make 22.08 L at 20 °C. At 80 °C, the shrinkage is 2.64%.
And with the assistant?
Ask Krausi the same question in plain language: he picks this tool, does the calculation and files the result in your project.
I have 25 L in the kettle at 80 °C, how much will that be once chilled?
At 20 °C you will have 24.34 L left (2.64% shrinkage). I'm noting 24.3 L as the end-of-boil volume of the brew.