How To Use A Hydrometer

Posted on April 5, 2010 by

What the heck is this little do-hicky that came with my homebrewing starter kit and what does it do, and WORST yet, how the hell do I use it?

This interesting little tool is called a hydrometer and comes in real handy for beginner, novice, advanced and expert homebrewers. The hydrometer has two main purposes. It tells you when your beer is done fermenting and it tells you how much alcohol is in your new beer. But how do you use a hydrometer? Let’s discuss.

How To Use A hydrometer

First things first. We need to learn how to take a reading. With a little direction, you’ll be an expert scientist in no time!

How to use a hydrometer

Drink you sample or discard it, but never put it back into the fermenter. Now what do you do with that reading?

Use it to find out when your fermentation is complete.

1. Take a sample of beer and place it in the tube that your hydrometer came in after you are done brewing and aerating your wort. This is done before pitching your yeast. Make sure you use a sanitized wine thief or other tool to acquire your sample. Mark that number down in your brewing notes. You will use this number to figure out ABV and if your fermentation is complete.

2. When you start to think fermentation is complete, take another sample. Again, be sure to use a sanitized wine thief or other tool to acquire your sample.

3. Measure that sample and note the number. Do not put the sample back into your fermenter!

4. Twenty-four hours later, take another sample and note that number.

5. Another 24 hours later, take another sample, note that number. If your number has not changed over 3 days your fermentation is complete and you are ready to bottle.

Use your hydrometer to tell how much alcohol by volume is in your beer.

1. Remember that first reading you took when you brewed up your batch of beer? Bring that number out because you’ll need it to figure out the final alcohol content.

2. Take a final sample from your bottling bucket. Once you moved your brew over go ahead take a sample right out of the spigot or use the number from step 5 where you determined your fermentation was complete.

3. Take a reading like describe above.

How to Calculate Alcohol By Volume

Calculating the alcohol content of your beer can be pretty easy if you just follow the following formula.

(Original Gravity – Final Gravity) X 131 = ABV%

There you have it. You can now not only take an accurate hydrometer reading, but you can use this tool to find out when your fermentation is complete and how much alcohol is in your beer!

Congratulations and happy brewing!

Side note:

Some people don’t bother using hydrometers and that is perfectly fine and dandy. They just like to brew and have done it enough to know when their beer is done. On top of that, they have a pretty good idea of approximetly how much alcohol is in their beers or just plain do not care. However, if you are like me, you like to know these things for future reference as you tweak and formulate recipes. Regardless, any new homebrewer should pay attention and use their hydrometer until they are comfortable with knowing when fermentation is complete. Otherwise, you may end up with some bottle bombs and those are no fun.

Just remember, have fun and enjoy!

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  • Tantilloon

    Nice diagram! Very helpful. My hydrometer came in a flimsy plastic container (flexible and thin.) It is definitely water tight, but seems like it might leach something into the beer. Is this typical of the test tubes? Should I toss the sample after taking the reading?

  • mikebiewer

    Thanks! Glad it served its purpose.

    As for putting it back into the beer or wort, don't do it. Once you take a sample, keep it out. Personally I drink it. I don't care if its sweet wort or flat fermented beer. It all tastes good to me and gives me insight as to some of the changes that take place along the process. I'd recommend giving it a taste as well.

    Whatcha brewing up these days?

    Thanks for the comment!


  • Tantilloon

    I'm brewing up some Red Ale this Sunday. It'll be my first solo project, so I hope I can prevent the boil-overs! (Using a turkey fryer.) I'll try tasting the samples for this batch, thanks for clearing that up!

  • mikebiewer

    No problem!

    If you have any other questions, feel free to ask them. Good luck on your first solo batch!

    Maybe you'll want to participate in the “First Time Homebrewer” interview series after you taste your first bottle?

    For more info, check the First Time Homebrewer.

    Where did you get your Red Ale kit from? Its a kit right?

    Thanks for following up!


  • Brett

    The diagrams are helpful, Mike. I feel I usually end up guessing what reading the hydrometer is showing because its floating around in the bucket, foam gets in the way, the measurement lines are so small … and usually I've been brewing all afternoon and just want to be done with it.

    A friend of mine has a lab where he gets his wort scientifically testing for ABV. Not nearly as fun as guessing.

  • mikebiewer

    Thanks for stopping by!

    I'm glad you found the information to be somewhat useful. I've been told that I should get a “refractometer”, but unfortunetly I'm unable to afford such commodities at this point in my brewing career. I do recommend taking samples and not just leaving the meter in there. This way you can taste it along the journey of becoming beer as well!

    Again, thanks for stopping by!


  • carpet cleaning melbourne

    Great beginners guide for consistent results!

  • MKassal

    thanks for the tip… I am getting back into brewing, and in the past it was always Pop’s job to do the calculations,,,

  • Anonymous

    No problem!

    Let me know if there is anything I can help with.


  • ESawyer

    Great tips! To the point. Quick question though… since I didn’t read up too much on the hydrometer prior to pitching the yeast, I didn’t take a reading then. Now my beer has been fermenting for a week and a half already. Any way to figure out ABV still? I can still measure specific gravity to make sure no “bottle bombs” happen I guess…

  • SYAGER48

    I hate to ask this but in your mag view what is the reading ~1.008 ?

  • mike

    so, im very new at this what could happen if you put the brew you took out to test back in?

  • Peace

    so if my hydrometer is leveled after the last # possible…….what should I count that answer as?

  • pops

    I have the same question as Syager48 below but I didn’t see a reply. What the numbers on the hydrometer mean. As in the numbers 10, 20, 30 below the number 1.000 in your magnified view. For example, does the 10 mean 1.10 or 1.01 or 1.001? Again, in your picture, does that mean 1.008?

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