How To Read A Hydrometer: 15 Steps (with Pictures) - WikiHow

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Terms of Use wikiHow is where trusted research and expert knowledge come together. Learn why people trust wikiHow How to Read a Hydrometer PDF download Download Article Explore this Article parts 1 Taking a Reading 2 Testing Your Hydrometer Other Sections Questions & Answers Video Tips and Warnings Related Articles References Article Summary Co-authored by Joseph Quinones

Last Updated: December 17, 2025 Fact Checked

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This article was co-authored by Joseph Quinones. Joseph Quinones is a Physics Teacher working at South Bronx Community Charter High School. Joseph specializes in astronomy and astrophysics and is interested in science education and science outreach, currently practicing ways to make physics accessible to more students with the goal of bringing more students of color into the STEM fields. He has experience working on Astrophysics research projects at the Museum of Natural History (AMNH). Joseph recieved his Bachelor's degree in Physics from Lehman College and his Masters in Physics Education from City College of New York (CCNY). He is also a member of a network called New York City Men Teach. There are 8 references cited in this article, which can be found at the bottom of the page. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 248,122 times.

A hydrometer is a measurement tool, usually made from a weighted glass tube, used to test the density of a liquid. The idea behind the hydrometer is that suspending a solid object in a liquid will cause the solid to float to the same degree as the weight of the displaced fluid. This means the tool will sink lower in a less dense 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.

Steps

Part 1 Part 1 of 2:

Taking a Reading

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  1. Step 1 Check your hydrometer's temperature calibration. 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. Step 2 Measure the temperature of the liquid. 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 at the end of this article.
    • 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.
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  3. Step 3 Pour a sample into a clean container. 3 Pour a sample into a clean container. Choose a transparent jar or cup large enough that the hydrometer can float without hitting the sides or bottom of the container. Transfer a sample of the liquid into this container.
    • When brewing, test the wort after visible signs of fermentation have ended, but before pitching the yeast. Transfer the sample using a sanitized siphon, wine thief, or baster.[1]
    • If precision is extremely important, rinse the container with a small amount of the liquid before adding the full sample.
  4. Step 4 Insert the hydrometer into the liquid. 4 Insert the hydrometer into the liquid. Make sure the hydrometer is dry, then lower it into the liquid just below the point at which it would float naturally. Be sure the hydrometer bulb does not touch the sides or bottom of the jar when it settles.
  5. Step 5 Spin the hydrometer gently. 5 Spin the hydrometer gently. This will dislodge air bubbles clinging to the tool, which would disrupt the measurement. Wait for the hydrometer and the liquid to stop moving, and for bubbles to dissipate.
  6. Step 6 Read the hydrometer scale at the lowest point of the liquid's surface. 6 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. Look for the scale mark on the hydrometer level with the lowest point on the fluid's surface. Do not use the mark where the fluid touches the hydrometer.[2]
  7. Step 7 Understand the measurement. 7 Understand the measurement. The most common scale on hydrometers is "specific gravity." This is the ratio of the liquid's density to the density of water. Pure water should give a reading of 1.000. A higher reading means the liquid is denser (heavier) than water, and a lower reading means it is lighter.
    • 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 alcohol content in the final beer. Most beers OGs fall in the 1.030 to 1.070 range, but they can be significantly higher.[3]
  8. Step 8 Interpret the Plato, Balling, or Brix scales. 8 Interpret the Plato, Balling, or Brix scales. Your hydrometer may use one of these scales instead, or you may need to convert your measurement to follow a certain recipe. Here's how to measure density using these three units:
    • The Plato scale measures the percentage of sucrose in a wort, so 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 degrees 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.[4] )
    • The Balling and Brix scales measure the sugar concentration in a solution, but the units are close enough to the Plato scale that you can use them interchangeably for home brewing. Commercial breweries use more exact conversion formulas, and conduct their own tests to calibrate the Brix scale based on various factors.[5]
  9. Step 9 Take a reading of the final brew. 9 Take a reading of the final brew. At the end of the entire brewing process, test additional samples daily with the hydrometer. If the reading is the same two days in a row, no more sugars are being converted into alcohol, meaning fermentation is complete. The final reading at this point is the "final gravity" or "FG." The target FG depends on what kind of brew you are making, and in some cases on additional ingredients that affect the hydrometer reading.
    • With a few exceptions, most beers have an FG around 1.007 to 1.015.[6]
    • Home brewers rarely get the exact FG predicted by their recipe, especially on their first few attempts. It's more important that the beer tastes good, but keep records and keep studying the process to get a more consistent result.
  10. Step 10 Estimate alcohol by volume. 10 Estimate alcohol by volume. The difference between the original gravity and final gravity tells you how much sugar was converted to alcohol. The formula 132.715 x (OG - FG) is a useful way to convert this into alcohol by volume (ABV). Note that this is only an estimate, and is most accurate for beers with a final gravity around 1.010.[7]
    • For example, if your OG was 1.041 and your FG is 1.011, the ABV is roughly 132.715 x (1.041 - 1.011) = 3.98%.
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Part 2 Part 2 of 2:

Testing Your Hydrometer

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  1. Step 1 Fill a container with water. 1 Fill a container with water. To test whether the hydrometer is accurate, 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.
  2. Step 2 Bring the water to the correct temperature. 2 Bring the water to the correct temperature. The hydrometer's calibrated temperature should be marked on the hydrometer label or the package instructions.
  3. Step 3 Measure the density of the water. 3 Measure the density of the water. Place the hydrometer in the water, spin gently to shake off air bubbles, and wait for it to settle. 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.
    • See the instructions above for a more detailed guide on how to use the hydrometer.
  4. Step 4 Write down the correction if the hydrometer is inaccurate. 4 Write down the correction if the hydrometer is inaccurate. If you get a result other than 1.000, the hydrometer is off (or your water contains minerals). Write down the amount you need to add or subtract to future readings to correct this error.[8]
    • 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.
  5. Step 5 Consider replacing or adjusting your hydrometer. 5 Consider replacing or adjusting your hydrometer. 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, but it is possible for the frugal brewer to correct it:[9]
    • 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 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. 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 Yes No Not Helpful 3 Helpful 14
  • Question How do you find the percentage of sugar from the specific gravity reading? Community Answer 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. 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 Yes No Not Helpful 4 Helpful 5
  • Question Can I use a hydrometer to test the salt content of water? Community Answer 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 Yes No Not Helpful 2 Helpful 3
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Video

Temperature Adjustment

  • Adjust temperature for a standard hydrometer. If your hydrometer is calibrated for 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: ( T e m p ( F ) T e m p ( C ) S G a d j u s t m e n t 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 ) {\displaystyle {\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}}}

Tips

  • Commercial brewers measure density frequently during brewing, and keep detailed records in order to track inconsistencies or the results of different methods.[10] That said, there's a risk of contamination each time you open the lid. In a home environment, it's usually best to check on the beer as little as possible. Thanks Helpful 0 Not Helpful 0
  • Brewers usually pronounce specific gravity readings as two 2-digit numbers. For example, a reading of 1.072 is called "ten-seventy-two." Thanks Helpful 1 Not Helpful 0
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Warnings

  • 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. Thanks Helpful 1 Not Helpful 0
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References

  1. ↑ https://grainfather.com/forced-fermentation-test-what-is-it-and-why-do-it/
  2. ↑ https://www.homebrewersassociation.org/how-to-brew/how-to-take-an-accurate-hydrometer-reading/
  3. ↑ https://www.homebrewersassociation.org/how-to-brew/how-to-take-an-accurate-hydrometer-reading/
  4. ↑ http://byo.com/stories/item/411-calibrate-your-hydrometer-and-fermenter-techniques
  5. ↑ http://byo.com/hops/item/1313-refractometers
  6. ↑ http://www.brewersfriend.com/2009/02/04/beer-styles-original-gravity-and-final-gravity-chart/
  7. ↑ http://learn.kegerator.com/specific-gravity/
  8. ↑ https://byo.com/mead/item/411-calibrate-your-hydrometer-and-fermenter-techniques
  9. ↑ https://www.homebrewersassociation.org/how-to-brew/how-to-take-an-accurate-hydrometer-reading/
More References (1)
  1. ↑ https://www.craftbeer.com/craft-beer-muses/defining-gravity

About This Article

Joseph Quinones Co-authored by: Joseph Quinones Physics Teacher This article was co-authored by Joseph Quinones. Joseph Quinones is a Physics Teacher working at South Bronx Community Charter High School. Joseph specializes in astronomy and astrophysics and is interested in science education and science outreach, currently practicing ways to make physics accessible to more students with the goal of bringing more students of color into the STEM fields. He has experience working on Astrophysics research projects at the Museum of Natural History (AMNH). Joseph recieved his Bachelor's degree in Physics from Lehman College and his Masters in Physics Education from City College of New York (CCNY). He is also a member of a network called New York City Men Teach. This article has been viewed 248,122 times. 72 votes - 63% Co-authors: 15 Updated: December 17, 2025 Views: 248,122 Categories: Chemistry Article SummaryX

To read a hydrometer, pour a sample of the liquid you want to test into a clean, transparent container. Lower the hydrometer into the liquid and stir it around gently, but make sure it doesn’t touch the sides of the container. Read the hydrometer scale at the lowest point of the surface of the liquid. The most common scale on hydrometers is specific gravity, in which pure water measures 1.000. If you get a higher reading, your liquid is heavier than water, and if you get a lower reading, it’s lighter. Keep reading for tips from our reviewer on how to read Plato, Balling, or Brix scales. Did this summary help you?YesNo

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Reader Success Stories

  • D. Newman

    D. Newman

    Oct 23, 2017

    "Straightforward explanation of the scales and the calculations of ABV were helpful. Thank you very much."
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Did this article help you?

Yes No Advertisement Cookies make wikiHow better. By continuing to use our site, you agree to our cookie policy. Joseph Quinones Co-authored by: Joseph Quinones Physics Teacher 72 votes - 63% Click a star to vote Co-authors: 15 Updated: December 17, 2025 Views: 248,122 D. Newman

D. Newman

Oct 23, 2017

"Straightforward explanation of the scales and the calculations of ABV were helpful. Thank you very much." Rick Thomas

Rick Thomas

May 9, 2020

"I now understand how to read the hydrometer and work out the approximate alcohol content. Thank you." Mahdi Zamaniyan

Mahdi Zamaniyan

Oct 21, 2018

"That helps me so much, now I can measure the alcohol percent exactly! Thank you very much!" Share yours! More success stories Hide success stories

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