How to Use a Hydrometer in 4 Easy Steps


What is a Hydrometer?

A hydrometer is a basic tool that is used to measure the ratio of a sample liquid’s density to the density of water. In home brewing, it is a necessary tool that will show you the degree to which the yeast is converting sugar into ethanol, ultimately helping you gauge the health and success of your beer’s fermentation.

Why do I need a Hydrometer to make beer?

Homebrewing isn’t a cakewalk. There is a lot of time and effort that goes into it and there are many opportunities for things to go wrong. Perhaps the most important (and delicate) stage within beer making is fermentation. That is exactly why a hydrometer is so important, as it is the device that will tell you how the fermentation process is going. A hydrometer can be the single tool that alerts you of issues during fermentation, allowing you to make adjustments as needed.

How do I use a Hydrometer?

Using a hydrometer isn’t as complicated as you might think. It’s a simple 4-step process:

1. Retrieve Sample & Insert Hydrometer

You will need to take your first measurement after the cooldown, prior to pitching the yeast. The reading that you will get is called the original gravity, often referred to as “OG”.

To obtain this reading, first use a beer thief to retrieve a sample of the wort and transfer it to a testing jar or cylinder. The testing container should have enough liquid in it to fully suspend the hydrometer. After transferring a sample to your test container, place the hydrometer in the wort and allow it to buoy. Wait until all air has escaped from the liquid or gravitated upward. From there it is recommended that your hydrometer be centered and vertically positioned so it can depict the most accurate reading.

2. Obtain the Original Gravity Reading

Beer & Hydrometer

The increments of your hydrometer represent specific gravity points. The level to which the liquid rises is where your gravity reading should occur (we’ll call this the liquid-air line). At this point, record the number on your hydrometer that is being crossed by the liquid-air line. A typical wort OG will be between 1.035 and 1.060. Your ingredient kit will list an OG so that you’ll have a reference for what your wort’s OG should be close to.

Note: To get the most accurate data, read the bottom of the meniscus – as in where the liquid is level and not pulled by tension up the sides of the container or hydrometer itself

3. Calculate with Temperature

Hydrometer readings are stated assuming a standard temperature of 15°C (59°F), so knowing the temperature of your wort is crucial for an accurate reading. If your temperature reading is different, be sure to calibrate.

Calculate the difference by using the table below. Simply add the “△ Gravity” to your initial reading to obtain the correct specific gravity.

Hydrometer Temperature Correction

°C °F △ G °C °F △ G
0 32 0.0007 25 77 0.0021
1 33.8 0.0008 26 78.8 0.0023
2 35.6 0.0008 27 80.6 0.0026
3 37.4 0.0009 28 82.4 0.0029
4 39.2 0.0009 29 84.2 0.0032
5 41 0.0009 30 86 0.0035
6 42.8 0.0008 31 87.8 0.0038
7 44.6 0.0008 32 89.6 0.0041
8 46.4 0.0007 33 91.4 0.0044
9 48.2 0.0007 34 93.2 0.0047
10 50 0.0006 35 95 0.0051
11 51.8 0.0005 36 96.8 0.0054
12 53.6 0.0004 37 98.6 0.0058
13 55.4 0.0003 38 100.4 0.0061
14 57.2 0.0001 39 102.2 0.0065
15 59 0 40 104 0.0069
16 60.8 0.0002 41 105.8 0.0073
17 62.6 0.0003 42 107.6 0.0077
18 64.4 0.0005 43 109.4 0.0081
19 66.2 0.0007 44 111.2 0.0085
20 68 0.0009 45 113 0.0089
21 69.8 0.0011 46 114.8 0.0093
22 71.6 0.0016 47 116.6 0.0097
23 73.4 0.0016 48 118.4 0.0102
24 75.2 0.0018 49 120.2 0.0106

4. Repeat to Obtain Final Gravity Reading

You’ll want to take another hydrometer reading when the fermentation process is complete or nearing its end. By the way, with an alcoholic content, it is now officially beer and no longer wort. This reading will be the final gravity, or “FG” and should be close to the listed FG, which is included in your ingredient kit instructions. To give you a good idea of what to look for, a typical beer’s FG is between 1.015 and 1.005 and should be about 1/4th or 1/5th of the beer’s OG.

Careful, Don’t Overdo It

A lot of beginners make the mistake of testing their brew too often. Remember that each time you test you are running the risk of exposing your beer to harmful air or bacteria, which can ruin an entire batch. We recommend only testing once before pitching and once after fermentation is believed to be complete. If additional testing is needed, perhaps due to stuck fermentation, do your best to use extreme caution.

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Jeff Flowers

About Author

Jeff Flowers has been a self-described beer geek for over a decade now. When he's not chasing his daughter around, you can usually find him drinking a fresh brew and wasting too much of his time on both Google+ & Twitter.


    • Jeff FlowersJeff Flowers says

      Hi Sandy,

      I would assume you have looked for cracks or some sort of flaw that would prevent it from working as it is intended to. So, I’ll skip the potentially obvious problems.

      If it is completely submerged into your beer, it may just be defective. Depending on how long you’ve had it, I would suggest you attempt to return or exchange it from wherever you bought it from. But, a new hydrometer (or even upgrading to a refractometer) is something you will need to think about.

      If the hydrometer wasn’t floating because it was touching the bottom of the test tube, then it is likely that the sample you pulled was too small. Surprisingly, this is a common problem. In this case, you would just need to test a larger sample and see if the hydrometer works as it should.

      No matter what, I would also recommend testing your hydrometer in water. This will give you a better idea of how accurate its readings are.

      Please let me know if these tips work, as well as updating me on the solution you found.


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