Temperature correction calculator
Correct a hydrometer proof reading taken off 60 °F to its true proof at 60 °F.
A proof hydrometer only reads true at 60 °F. Take the reading warmer and it reads low; take it colder and it reads high. The Temperature Correction calculator turns the reading you actually took, at the temperature you took it, into the true proof at 60 °F — the figure every other proof-gallon calculation expects. It follows 27 CFR §30.61 (Table 1).
It's free, needs no account, and computes in your browser.
Open the calculator
- On the public site: in the top navigation choose Tools, then on the Temperature Correction card choose Open calculator.
- Inside the app: in the navigation choose Tools, then on the Temperature Correction card choose Open calculator.
Correct a reading to 60 °F
- In Hydrometer reading (proof), enter the proof your hydrometer showed — a number from 0 to 200.
- In Temperature (°F), enter the temperature you took the reading at, in degrees Fahrenheit (the correctable range is 0–100 °F).
- True proof (at 60 °F) appears as soon as both fields hold valid numbers.
If a value is outside its field's range, that field shows a hint (Enter a proof between 0 and 200. or Enter a temperature in °F (0–100).). If the reading and temperature don't describe a real ethanol-water mixture — a physically impossible pair — the calculator says so plainly (That reading and temperature are out of range for this correction…) rather than inventing a number. Check your values and try again.
Worked example
A hydrometer reads 193° proof, taken at 75 °F:
- Hydrometer reading (proof):
193 - Temperature (°F):
75
The calculator shows True proof (at 60 °F) 189.5 — the warm reading corrected down to its true value.
When to reach for it
Reach for Temperature Correction any time you gauge proof somewhere other than 60 °F, before you use that proof anywhere else — feed the corrected true proof into the Proof gallons calculator or the Weight-to-proof-gallons calculator, never the raw warm-or-cold reading.
A note on this calculator's accuracy. Instead of reading the official printed §30.61 Table 1 cell by cell, this calculator computes the correction from the underlying ethanol-water density model, so it gives a result for any in-range reading. It's anchored to the example values the regulation prints and matches them; a full independent check of the computed results against the complete official table is still under review. Treat it as a reliable reference estimate — the calculator itself notes it's a tool, not an official TTB filing or gauge record.