I’m struggling (again) to make sense of my Hydrometer. I am brewing an American IPA from a kit. I started on Sunday and before pitching the yeast I took a reading (photo 1), I had 24 hours crazy fermentation, then nothing. Barely a bubble. Today (Thursday - Day 4) I took anther reading (photo 2). Something has definitely happened and it floats a lot lower! I am meant to be adding hops on day 7 and tasting it on day 10. Am I on track with this reading?

Also, sorry for the really basic question, but why does my potential alcohol scale on my hydrometer appear to go in reverse I.e it started at 6% and is now nearer 0% after fermentation?


Original reading

Day 4 reading

2 Answers 2


To expand a little bit on @czernina's correct answer:

Hydrometers measure specific gravity, defined as the ratio of the density of a substance to the density of a given reference material.

In our case, the reference material is plain water at 60 degrees F, which we read as 1.000. So the closer we are to 1.000, the less sugar is left in solution. The higher the number, the more sugar is in solution.

You do need to make sure your wort sample is cooled to around 60F. You can use a chart to adjust your reading based on temperature, but in my experience the closer you get to 60, the more accurate your readings will be.

Looking at your first picture, your reading is 1.056. This would be your starting gravity or original gravity.

Your second reading looks 1.016. This would be your final gravity, assuming your yeast has finished eating all the sugar it wants to.

Side note: if you want to be sure the yeast is done doing its thing, take another gravity reading in a few days and see if it changes. If it hasn't, then you know your beer is done fermenting.

Why is your final gravity lower? Because your yeast has consumed much of the sugar in your wort and converted it to alcohol (and CO2, but most of that bubbled off into the atmosphere). Your wort has less sugar, so is less dense, so your hydrometer doesn't float as high.

Now to calculate the alcohol from these numbers is a little complicated (you can't just use the % on the hydrometer), so use your favorite search engine and find a beer ABV calculator, like this one at Brewer's Friend. Or do what I do and use software like Beersmith to do all the calculations for you.

It will tell you that your ABV is a little over 5%.

Gravity Action

  • That is really helpful. Thank you so much for taking the time to explain that. Very helpful.
    – Andrew F
    Oct 22, 2020 at 8:08

I'm not sure how to answer your first question, but I can answer your second question. A hydrometer doesn't measure potential alcohol; that's something we as the user derive from the information. What the hydrometer does do is measure the gravity (density) of the wort. Starting at 1.000 is water, but because sugar is heavier than water, any added sugar raises the density. A hydrometer allows us to quantify how much change in density has occurred, thus telling us how much alcohol has been made and sugar consumed by the yeast. That is why your hydrometer scale appears to go in reverse, because the yeast are making the liquid less dense through consumption of sugar and producing an alcoholic solution.

  • 1
    Aha! I understand now. So my orignal reading had. a reading of 7% and my latest reading is about 1% so my alcohol content is approx 6% (plus or minus the alteration made for temperature etc.)? Thank you for explaining that.
    – Andrew F
    Oct 15, 2020 at 19:55

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