# Correct temperature effect on Specific gravity

Is there an equation that corrects specific gravity while considering temperature effect in Celsius, which does not presupposes a set hydrometer calibration temperature?

A direct relation, not tables or something static. And if there is one, where would you find it?

A similar question was asked Here, but the answers are all in Fahrenheit or assume a 15 C (59 f) calibration temperature.

Quick but not very helpful answer, I am pretty sure there is some sort of equation that can be used for this I am not sure where I have seen it. I am going to do some digging through some book and the interwebs for you and will update here if/when I find it.

Found it, it assumes T is in C.

SG(true) = SG(indicated) x [ 1.0 - 0.00025[ T(actual) - T(calibrated) ]]

• just tried it with a couple of online calculator and it seems to marry up, once I corrected the out by a power of 10 error, also I am not sure if T(a) andT(c) are the right way round, but in 2 quick tests it agrees with other calculators that have proven accurate for me over time.
May 12, 2018 at 17:25
• Sounds promising - gonna run a few quick tests, but it looks really good! Thanks Mr_road! May I ask where you found it? May 12, 2018 at 17:33
• I did some googling then fixing, will dig it out and add it to answer.
May 13, 2018 at 12:41
• That's great - looking forward to hearing from you, road! May 14, 2018 at 17:53

It actually depends on the hydrometer. They can vary a lot beween makers. Each one has thier own temperature adjustment chart. Because they can have different displacements and scales on them.

It depends on the hydrometer. Older hydrometers tend to be calibrated at 15C (59F), and more recent ones at 20C (68F).

Yes, there has been some attempts to correct for an offset in temperature. Check out https://www.brewersfriend.com/hydrometer-temp/ for more details.

Anyways, I’d guide against measuring at a different than the calibrated or recommended temperature. This is because warm wort might shatter a glass hydrometer causing small metal balls to leak. I assume they are made from lead. Or even worse, it might crack the glass making it hard to discover. Additionally, in my personal experience measuring hot wort generally produce inaccurate readings even when trying compensate for the temperature.

I cool my wort to around 23 degC before taking a reading. Only takes a few minutes to cool a test tube from 100 degC to 23 degC

• While the first answer is technically correct, I consider this answer practically correct. Always cool the wort you are measuring. I use a metal beaker and water with ice cubes. While you are mashing you obviously have a thermometer at hand. May 16, 2018 at 12:42
• With "practically" meaning "in practice", not "almost". May 16, 2018 at 12:54