Brewing Hydrometer Correction

Enter three values: your measured specific gravity reading, the temperature of your sample when you took the reading, and the calibration temperature printed on your hydrometer. The calculator returns the corrected gravity instantly and shows the size of the adjustment.

Use a kitchen thermometer or brewing thermometer in the sample jar — not the fermenter — so you measure the actual temperature of the liquid the hydrometer is floating in. Even a few degrees of difference between the sample and the jar changes the correction.

Liquids expand when heated and contract when cooled. A hydrometer measures density by how deeply it sinks, so when your sample is warmer than the calibration temperature the liquid is less dense, the hydrometer sinks deeper, and the scale reads lower than the true gravity. The reverse happens with cold samples.

The error is small per degree but adds up. A wort sample at 80 °F reads roughly two gravity points low on a 60 °F-calibrated hydrometer. If you take both OG and FG at different temperatures without correcting, the errors can stack or cancel unpredictably, making your ABV calculation unreliable.

Most brewing hydrometers sold in North America are calibrated to 60 °F (15.56 °C). European and laboratory-grade instruments often use 68 °F (20 °C). Some older or specialty models use 59 °F (15 °C). The calibration temperature is printed on the paper scale inside the hydrometer — check yours before correcting.

Using the wrong calibration temperature in the correction formula introduces a fixed offset on every reading. If you cannot find the marking, 60 °F is the standard default for homebrew hydrometers in the US and Canada.

Spin the hydrometer gently after placing it in the sample to dislodge CO2 bubbles clinging to the glass. Bubbles add buoyancy and make the reading appear lower than the true gravity. Wait for the hydrometer to stop bobbing before reading at the bottom of the meniscus — the lowest point of the curved liquid surface — at eye level.

Pull enough sample to float the hydrometer freely without it touching the sides or bottom of the test jar. Read the scale where the flat surface of the liquid crosses the stem, not where the meniscus climbs up the glass. A tall, narrow test jar makes this easier to see than reading directly in a wide container.