How to Use and Read a Hydrometer

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Measure the density of a brew and calculate ABV with this handy tool

Co-authored by Joseph Quinones and Amy Bobinger, BA

Last Updated: March 2, 2026 Fact Checked

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• Taking a Reading
|
• Reading Specific Gravity
|
• Interpreting the Plato Scale
|
• When to Read
|
• Adjusting the Temperature
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• Testing Your Hydrometer
|
• Video
|
• Q&A
|
• Tips

|Show more |Show less

A hydrometer is a measurement tool used to test the density of a liquid. Brewers use hydrometers to track the progress of beer or other fermented drinks, since the liquid's density decreases as yeast converts sugar into alcohol. We’re here with everything you need to know about hydrometers, including how to use one, how to interpret the readings, when to take measurements, and how to adjust for temperature.

How to Read a Hydrometer

1. Pour a sample of liquid into a trial jar.
2. Insert the hydrometer into the liquid and spin it to remove bubbles.
3. Take a reading at the bottom of the meniscus, or surface of the liquid.
4. Start your reading with the big number on the left of the scale (e.g., “1.0”).
5. Add the hundredths place from the 10s number nearby (e.g,. “1.02”).
6. Use the hash marks for the thousandths place. (e.g. “1.025”).

Steps

Section 1 of 6:

Taking a Hydrometer Reading

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1. 
   1
   Pour a sample into a clean trial jar. Graduated cylinders are perfect for this because they’re stable and don’t require a large sample. If you don’t have one, use a transparent jar or cup large enough that the hydrometer can float without touching the sides or bottom of the container. Carefully transfer a sample of the liquid into this container.

   • Some hydrometers come in a plastic tube that will double as a trial jar.
   • Transfer the sample using a sanitized siphon, wine thief, or baster.
   • Hydrometers are calibrated for use at a specific temperature. If you’re measuring a liquid that’s a different temperature than your hydrometer is calibrated for, check out our section on temperature adjustment below.
   • Never return a wort or beer sample back to the fermentation container after testing, or you could contaminate the batch. Taste it to see how the beer is coming along, then throw it away.
2. 
   2
   Insert the hydrometer into the liquid. Make sure the hydrometer is dry, then lower it into the liquid. Lower it gently, and try to release it at about the point where it would float (or its point of equilibrium). If the hydrometer splashes, you’ll have to wait for the liquid to stop moving before you can take a reading.

   • Be sure the hydrometer bulb does not touch the sides or bottom of the jar when it settles.
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3. 
   3
   Spin the hydrometer gently to remove bubbles. Spinning the hydrometer will help dislodge any air bubbles clinging to the hydrometer, which would disrupt the measurement. Wait for the hydrometer and the liquid to stop moving and for the bubbles to dissipate before you take your reading.
4. 
   4
   Read the hydrometer scale at the lowest point of the liquid's surface. The surface of the fluid may cling to the hydrometer and the container walls, forming a curve called a meniscus. Use the scale mark at the lowest point on the fluid's surface—not necessarily the mark where the fluid touches the hydrometer.

   • Some hydrometers have multiple scales. Most commonly, you’ll use the Specific Gravity (SG) scale, which is a reading of the density of the liquid you’re measuring.
   • The Brix scale and Potential Alcohol scales are both used to calculate the potential future alcohol percentage that an unfermented liquid might have. The Brix scale is more commonly used for large-scale operations, like commercial distilleries or breweries.
   • Some recipes may call for a Potential Alcohol reading, but the Specific Gravity reading is more accurate. The Potential Alcohol is based on a perfect fermentation where all of the sugar is converted into alcohol, which doesn’t always happen.
   • Check out the next section to learn more about interpreting a Specific Gravity reading.
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Section 2 of 6:

Interpreting a Specific Gravity Reading

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1. 
   1
   Start by looking for the big number on the left side. Look above the liquid line for the closest big number on the left side of the scale. On most hydrometers, these numbers are 0.9, 1.0, and 1.1. This will give you the ones and tenths places on your reading.

   • For instance, if your liquid falls just under the 1.0 line, your reading will always start with 1.0.
2. 
   2
   Look for the 10s number on the right side of the scale. On the right side of the scale, you’ll see lines marked with 10, 20, 30, etc. These numbers will give you the hundredths place of your reading.

   • For example, if your reading is near 1.0 on the left side and 20 on the right, it would be 1.020 (not 1.2).
3. 
   3
   Check the hash marks to finalize the reading. Between the 10s numbers, you’ll see a series of hash marks. These indicate the thousandths place of your reading. Each hash mark is .002.

   • Using the example above, if you’re at the third hash mark down, your final reading would be 1.026.
   • If you’re between the second and third hash marks, your reading would be 1.025.
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Section 3 of 6:

Interpreting the Plato Scale

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1. 
   The Plato scale measures the percentage of sucrose in a wort. Some hydrometers only measure using the Plato scale. 10 degrees on the Plato scale means 10% of the wort is sucrose by weight. Multiply the Plato measurement by 0.004 and add 1 for a specific gravity estimate that's close enough for homebrewing purposes.

   • For example, a 10-degree Plato wort has a specific gravity of 10 x .004 + 1 = 1.040. (The further you get from this number, the less accurate the conversion is.

Section 4 of 6:

When to Take Hydrometer Readings

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1. 
   1
   Take an Original Gravity (OG) reading at the start of fermentation. Take your first reading once you mix up your first batch of beer or wine—but before you add yeast. This is your Original Gravity (OG) reading. You’ll use this number to help you determine the final percentage of alcohol by volume (ABV) in your finished product.

   • The specific gravity of wort (called original gravity or OG by brewers) varies greatly. The more sugar in a wort, the higher the OG, and the higher the alcohol content in the final beer.
   • Most beers' OGs fall in the 1.030 to 1.070 range, but they can be significantly higher.
2. 
   2
   Use the hydrometer to determine when fermentation is finished. Once you stop seeing bubbles in your fermenter or airlock, test a sample with your hydrometer. Then, wait at least 1–2 days (up to about a week), and test again. If the readings were the same both times, fermentation is finished. The final reading is your Final Gravity (FG).

   • If the reading is lower the second time you test, wait a few more days and test again.
   • Be sure fermentation is completely finished before you bottle your brew. Otherwise, fermentation will continue. This can cause pressure to build up inside your bottles, potentially causing them to burst.
   • With a few exceptions, most beers have an FG around 1.007 to 1.015.
3. 
   3
   Estimate your ABV using the formula FG - OG * 131. Subtract your original reading (OG) from your final reading (FG). Then, multiply the result by 131. This is an estimate of your ABV, or the total percentage of alcohol in your final brew.

   • For example, if your OG was 1.041 and your FG is 1.011, the ABV is roughly 131 x (1.041 - 1.011) = 3.93%.
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Section 5 of 6:

Adjusting the Temperature

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1. 
   1
   Check your hydrometer's temperature calibration. Hydrometers measure the density of a liquid, but liquids expand and contract with temperature changes. To get an accurate answer, you need to test liquids at the temperature your hydrometer was designed for. This temperature should be listed on the hydrometer label, or on instructions in the same package.

   • Most homebrew hydrometers are calibrated at 59–60°F (15–15.6°C ), and most laboratory hydrometers are calibrated at 68°F (20.0°C).
   • Hydrometers can lose accuracy over time. If you're using an old tool, you may want to test it first.
2. 
   2
   Measure the temperature of the liquid. If this is more than a degree or two off from the hydrometer's intended temperature, write down the result. Your measurement will be off, but you can correct it using the temperature chart in the following step.

   • If testing homebrewed wort, do not contaminate it with a non-sanitized thermometer. Use an adhesive strip thermometer that sticks to the side of the container, or measure a sample instead of the main batch.
3. 
   3
   Adjust the temperature for a standard hydrometer. If your hydrometer is calibrated to 60ºF (15.6ºC), use the following chart when measuring at different temperatures. Find the temperature of the liquid in column 1 or 2, then add the number from the same row of column 3 to the specific gravity:
   
   ${\begin{pmatrix}Temp(F)&Temp(C)&SGadjustment\\50&10&-0.69\\55&12.8&-0.38\\60&15.6&0.00\\65&18.3&0.53\\70&21.1&1.05\\75&23.9&1.69\\80&26.7&2.39\\85&29.4&3.17\\90&32.2&4.01\end{pmatrix}}$
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Section 6 of 6:

Testing Your Hydrometer

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1. 
   1
   Take a reading of distilled water. To test your hydrometer, use distilled water or reverse osmosis water. If you use tap water or untreated bottled water in your brewing, you can test with that instead. The mineral content will alter the results, but this will tell you how to adjust your readings for brews made with that specific water.

   • Bring the water to the correct temperature. The hydrometer's calibrated temperature should be marked on the hydrometer label or the package instructions.
   • The hydrometer will read 1.000 for pure water if it is perfectly calibrated. A hydrometer that uses the Plato or Balling scale will read 0.00º.
2. 
   2
   Write down the correction if the hydrometer is inaccurate. If you get a result other than 1.000, the hydrometer is off. Write down the amount you need to add or subtract from future readings to correct this error.

   • For example, if your hydrometer reads 0.999 in pure water, add 0.001 to all measurements.
   • To take another example, if your hydrometer reads 1.003 in tap water, subtract 0.003 from all measurements of liquid brewed with that specific tap water. Test the hydrometer again if you change water sources.
3. 
   3
   Consider replacing or adjusting your hydrometer if the reading is off. If your hydrometer is significantly off, it's often best to order a new one. The old one may lose even more accuracy over time. That said, some people do attempt to correct their hydrometers instead of replacing them:

   • If the measurement is too low, attach tape, nail polish, or any other material to increase the weight until the measurement is correct.
   • If the measurement is too high, file the edge to remove material. Seal the rough area with nail polish to protect against glass dust or sharp edges.
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Community Q&A

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• Question

  What are the units of a hydrometer reading?

  

  Community Answer

  The most common scale, specific gravity, does not have units. It compares the density of the liquid to the density of water, so the result is in the form of a ratio or percentage. For example, a result of 1.050 means the liquid is 1.050 times as dense as water.

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• Question

  How do you find the percentage of sugar from the specific gravity reading?

  

  Community Answer

  A hydrometer with the Plato scale gives you the result directly: one degree Plato = 1% of sucrose by weight. To convert (roughly) from specific gravity to Plato, subtract 1, then divide by 0.004.

  Thanks! We're glad this was helpful.
  Thank you for your feedback.
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• Question

  Can I use a hydrometer to test the salt content of water?

  

  Community Answer

  Yes. You aren't testing the salt content per se, you're testing the density of the water compared to ideal, pure water. However, for all intents and purposes, if you're testing seawater, then you're testing the salinity by testing the density. Note that the density of water also changes with temperature (and to a lesser and irrelevant for your purposes degree, pressure). There are formulas to adjust your measurement based on temperature.

  Thanks! We're glad this was helpful.
  Thank you for your feedback.
  If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow

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Tips

• Brewers usually pronounce specific gravity readings as two 2-digit numbers. For example, a reading of 1.072 is called "ten-seventy-two."
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• There's a risk of contaminating your batch each time you open the lid, so it’s best to limit your readings as much as possible.
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