How to Use and Read a Hydrometer

by Dane Wilson | Last Updated: May 20, 2023

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Brewing beer at home is in equal parts an art and a science. The art comes into knowing which ingredients make the best beer, while the science comes into the precise measurements and temperatures required. Among those measurements is something called gravity, which you need when attempting to develop a certain kind of beer style. The specific gravity of ale, for example, is usually different from a stout. That is where the mighty hydrometer comes in. With this tool, you can figure out the gravity of the beer to see if it is done fermenting. As such, knowing how to read a hydrometer will come in handy.

That is why this guide has been created: To help you master the art of using a hydrometer when brewing up beer, mead, wine, or something else.

Table of Contents

how to read hydrometer

What is a Hydrometer?

Time to get a little technical. A hydrometer is a device used to measure the specific gravity (SG) of a liquid, which is the ratio of the density of that liquid to the density of water. It is commonly used in various industries, including brewing, winemaking, distilling, and chemistry.

The hydrometer consists of a narrow glass tube with a weighted bulb at the bottom and a graduated scale marked on the stem. The bulb contains a lead or tungsten weight to provide stability and ensure the hydrometer floats upright in the liquid being measured.

Hydrometers come in various types and are designed for specific purposes. They may have different scales, temperature correction factors, and ranges tailored to the industry or application in which they are used. It’s important to choose the appropriate hydrometer for the specific liquid and measurements required to ensure accurate results.

What Does a Hydrometer Do?

In brewing and winemaking, a hydrometer is essential for monitoring the progress of fermentation (learn more about the best fermentation chambers). By taking initial and final specific gravity readings, brewers and winemakers can calculate the alcohol content, measure the sugar content, estimate the fermentation progress, and make adjustments to achieve desired flavors and characteristics in the final product.

Aside from specific gravity, hydrometers can measure other things, including:

  • Potential Alcohol: This measurement is commonly used in winemaking and brewing. It indicates the potential alcohol content that can be achieved through fermentation. The potential alcohol scale on the hydrometer provides an estimation of the alcohol percentage by volume that can be produced from the sugar content in the liquid.
  • Brix: Brix is a measurement of the sugar content in a liquid, primarily used in the wine and fruit juice industry. It represents the percentage of sucrose by weight in a solution. Some hydrometers are specifically calibrated to measure Brix levels and provide a reading directly in degrees Brix.
  • Plato: Plato is another measurement of sugar content often used in brewing. It is similar to Brix and represents the percentage of extractable sugars in a solution by weight. Certain hydrometers are calibrated to measure the Plato scale and can provide readings in degrees Plato.
  • Potential Extract: This measurement is commonly used in brewing and indicates the potential extract or sugar content that can be obtained from the malt or other fermentable ingredients. It helps brewers calculate the potential yield and efficiency of their brewing process.

The above list is only for alcohol-brewing applications. Some hydrometers can be used for salinity, battery acid specific gravity, and so on. Make sure the hydrometer you are using is going to show the measurements that you need.

How to Read a Hydrometer Correctly

In order to properly read a hydrometer, you need to do a bit of prep work. The level at which the hydrometer floats in whatever liquid you are testing is how you interpret the specific gravity (SG) or other measurement.

Here is a step-by-step for how to read a hydrometer:

  1. Prepare the Sample: Take a sample of the liquid you want to measure, ensuring it is at the appropriate temperature specified for the hydrometer (usually around 68°F/20°C).
  2. Fill the Hydrometer Tube: Place the hydrometer in a tall, cylindrical container (such as a hydrometer jar) and carefully pour the liquid sample into the jar until it reaches a sufficient depth to float the hydrometer.
  3. Float the Hydrometer: Gently lower the hydrometer into the liquid, ensuring it is free from any obstructions and allowing it to settle and float freely.
  4. Read the Scale: Position yourself at eye level with the hydrometer and carefully read the scale where the liquid level intersects it. Take note of the specific gravity or measurement indicated by the hydrometer.
  5. Account for Meniscus: Pay attention to the shape of the liquid’s surface where it meets the hydrometer. The liquid’s surface may curve up or down around the edges, creating a meniscus. When reading the scale, align your reading with the bottom of the meniscus for accuracy.
  6. Correct for Temperature (If Required): If the hydrometer is not calibrated for the temperature of the liquid, you may need to apply a temperature correction factor specified by the hydrometer’s instructions or use a temperature correction chart to obtain an accurate reading. If you need to correct the temperature, there is an online calculator for that.
  7. Record the Measurement: Note down the specific gravity or other measurement reading for future reference, calculations, or comparisons during the brewing or winemaking process.

How to Use a Hydrometer When Making Beer

Now that you know how to read a hydrometer, let’s talk about putting it to good use. When making beer, a hydrometer is used to measure the specific gravity, or density, of the wort (unfermented beer) before and after fermentation. This measurement helps you, the brewer, to determine the alcohol content and to track the progress of the fermentation.

To use a hydrometer when making beer, you will first need to gather a sample of wort or beer for measuring. As a general guideline, you’ll want to collect enough beer to submerge the hydrometer fully without it touching the sides or bottom of the container. This ensures that the hydrometer can float freely and provide an accurate reading. Typically, a few ounces (around 4-8 ounces or 120-240 milliliters) of beer are sufficient for most hydrometer measurements.

It’s important to note that while you want enough beer for an accurate reading, excessive beer volume is unnecessary. You may end up with difficulties in handling the hydrometer or inaccurate readings due to insufficient submersion.

To avoid wasting precious beer, you can collect a smaller sample and gently pour it into the hydrometer sample jar, ensuring the hydrometer is fully submerged. If the hydrometer floats too high or too low, you can adjust the beer volume by adding or removing small amounts until it reaches the desired level.

Steps for Using a Hydrometer for Beer

Once you have collected your sample, follow these steps to acquire your reading:

  1. Sanitize the hydrometer and the vessel you will be using to collect the sample. (Read up on the best brewing sanitizer if you need some more.)
  2. Fill the vessel with enough wort or beer to allow the hydrometer to float freely. Again, the hydrometer should not touch any part of the container.
  3. Take a reading by placing the hydrometer in the liquid and giving it a spin to dislodge any bubbles that may be clinging to it.
  4. Read the hydrometer at eye level where the surface of the liquid meets the scale. Take note of the specific gravity reading on the hydrometer.
  5. After fermentation, take a second reading using the same process. The difference between the two readings will indicate the alcohol content of the beer.
  6. You can also use the hydrometer to monitor the fermentation process. Take readings at regular intervals and compare them to previous readings to track the progress of the fermentation.

You can also follow this video’s visual instructions:

Using a Hydrometer When Making Wine

Using a hydrometer when making wine follows a similar process to using it for beer, with a few differences specific to winemaking. When making wine, you can take hydrometer readings at different stages of the winemaking process, such as before fermentation, during fermentation, and after fermentation. These readings help monitor the progress of fermentation, estimate the alcohol content, and determine the sweetness or dryness of the wine.

It’s important to note that hydrometer readings in winemaking may be calibrated to specific scales, such as Brix or Potential Alcohol, depending on the region or winemaking tradition. Refer to the specific instructions provided with your hydrometer to interpret the readings accurately.

How to Read a Hydrometer When Making Mead

Although the process for reading a hydrometer when making mead is the same as you would do for beer or wine, there are some key differences between beer and mead that you must take into account.

First off, if you are making mead, you often dilute the honey with some water prior to fermentation. This is something you must factor in. It’s called dilution ratio. Using a hydrometer calculator online can help you figure out the dilution ratio. Secondly, mead requires a different temperature than beer for an accurate reading.

How to Use a Hydrometer For Moonshine

You know how to read a hydrometer by now, especially if you have brewed beer. But did you know you can use a hydrometer to monitor fermentation and measure estimated alcohol content of your moonshine, as well?

The process is the same:

  1. Sanitize your equipment, including the hydrometer before placing it in the moonshine sample.
  2. Let the hydrometer float freely, without touching the sides or bottom of the container.
  3. Read the hydrometer when the liquid meets the scale.
  4. If necessary, correct the temperature.
  5. Record the measurement.

What Are Some Common Mistakes to Avoid When Using a Hydrometer?

Learning how to read and use a hydrometer may seem straightforward, but there are a number of little mistakes that can throw your readings and calculators off. Here are some common hydrometer mistakes to avoid:

Inadequate Sanitization

Failing to properly sanitize the hydrometer and the container used for collecting the sample can introduce contaminants and affect the quality of your measurements. Make sure to sanitize all equipment thoroughly before use to maintain a clean and hygienic brewing environment.

Inaccurate Temperature Readings

Temperature plays a role in hydrometer readings. Most hydrometers are calibrated to a specific temperature, usually around 20 degrees Celsius or 68 degrees Fahrenheit. Failing to correct for temperature variations can result in inaccurate readings. Use temperature correction charts or calculators provided with the hydrometer to adjust the reading to the correct temperature.

Air Bubbles

Air bubbles or carbonation clinging to the hydrometer can cause it to float higher or lower than it should. When that happens, the numbers you see may be incorrect. Gently spin the hydrometer or use a clean stirring rod to dislodge any bubbles before taking a reading.

Insufficient Sample Volume

Not having enough liquid in the container to fully immerse the hydrometer can affect its buoyancy. That may lead to inaccurate readings. Ensure that the sample volume is sufficient enough to submerge the hydrometer without it touching the sides or bottom of the container. Again, the usual sample size is around 4-8 ounces or 120-240 milliliters.

Contamination from Sample Transfer

If the sample is transferred from one container to another, improper pouring or transfer techniques can introduce contaminants or cause splashing. This affects the integrity of the sample and subsequent readings. Handle the sample with care, avoiding unnecessary agitation or exposure to potential contaminants.


Reading the hydrometer from an incorrect angle can distort the reading and lead to inaccurate results. Always read the hydrometer at eye level, ensuring that the liquid level meets the scale directly.

Put Your Hydrometer to Work

Knowing how to read a hydrometer and using it correctly can make your homebrewing process much easier, especially when you want to zero in on a specific gravity. You also gain insights into the sugar content and potential alcohol yield of your liquids. This knowledge empowers you to monitor fermentation progress, make informed decisions during the brewing or winemaking process. Ultimately, you will create higher-quality beverages. Cheers to your brewing adventures!

Frequently Asked Questions

How do you read hydrometer results?

To read hydrometer results, carefully place the hydrometer into the liquid sample. Ensure that it floats freely without touching the sides or bottom of the container. Read the scale at eye level where the liquid level intersects with the hydrometer. Note the specific gravity or other measurement indicated on the scale. Correct the reading for temperature if necessary, using a temperature correction chart or instructions provided with the hydrometer.

What do the numbers on a hydrometer mean?

In the context of brewing or winemaking, the numbers on a hydrometer indicate the sugar content and potential alcohol yield. The numbers on the hydrometer scale correspond to specific gravity values, potential alcohol percentages, Brix (sugar content), Plato (sugar content in brewing), or other relevant units of measurement, depending on the specific hydrometer type.

Can a hydrometer be used for other purposes besides measuring alcohol content?

Yes, a hydrometer can be used for various applications beyond measuring alcohol content. It is commonly used in winemaking, cider production, brewing beer. Hydrometers are even used in some scientific and industrial processes where liquid density or concentration needs to be determined.