# Hydrometer Temperature Correction

Calibration temp (°C)

Details:  The density of water changes predictably with temperature and so it is possible (and important) to correct readings taken at temperatures the hydrometer is not calibrated for.  Most hydrometers are calibrated to 20°C, but some are calibrated to 15°C - any good hydrometer will have the calibration temperature marked.
This calculator, when working with a hydrometer calibrated to 20°C, is accurate over the approximate range 0-60°C, and when calibrated to 15°C, approximately 0-55°C.

The hydrometer temperatre correction for SG is performed with this expression:

corrected-reading = r * ((1.00130346 - (0.000134722124 * t) + (0.00000204052596 * t2) - (0.00000000232820948 * t3)) / (1.00130346 - (0.000134722124 * c) + (0.00000204052596 * c2) - (0.00000000232820948 * c3)))

Where:
c = calibration temperature

This expression is based on °F, so the temperatures are first converted.

For °Brix, the expression used is:

correction = 0.0000006907947565 * temp4 + 0.0000008650898228 * temp3 * apb + 0.0000002111610273 * temp2 * apb2 - 0.000000420289855 * temp * apb3 + 0.0000000000000000003388131789 * temp4 - 0.00002646880494 * temp3 - 0.00003812273795 * temp2 * apb + 0.00002132555958 * temp * apb2 + 0.0000003140096619 * apb3 + 0.001470413886 * temp2 + 0.0003854292164 * temp * apb - 0.00001254869767 * apb2 + 0.04799327348 * temp + 0.0002013056055 * apb - 0.002157758291

Where:
correction = is the correction factor, added to the observed °Brix
temp = is the temperature difference from calibration (that is, reading temperature - calibration temperature)
apb = is the apparent °Brix, as read on the hydrometer

VinoCalc by Jonathan Musther  -  jon@musther.net