How to Use and Read a Hydrometer: Ultimate Guide | Linquip (2024)

You might already know that a hydrometer is a device that is used to measure the specific gravity, or in other words, the relative density of liquids. And that is a good start, but do you know how to use and read a hydrometer?

In this article, you will first get a brief introduction to what hydrometers are to get a better sense of how to use and read a hydrometer.

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How to Use and Read a Hydrometer: The shortest story

A hydrometer is a device usually made of glass, which consists of a cylindrical stem and a bulb weighted with mercury or lead shot to make it float upright. As already mentioned, it is used to measure the specific gravity of liquids, i.e. the ratio of the density of the liquid to the density of water.

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A hydrometer operates according to the Archimedes principle stating that a solid-state body displaces its own weight with a liquid in which it floats. The liquid to be tested is poured into a tall specially designed cylindrical container, and the hydrometer is gently lowered into the liquid until it freely floats. There is a point at which the surface of the liquid touches the stem of the hydrometer. This point is noted as the reading point.

These devices usually have a scale inside the stem by which the specific gravity is read. There could be a different scale inside the stem depending on the context of usage. These scales include Specific Gravity (SG), Brix, Baume, and Alcohol. In the specific gravity or standard hydrometer scale, distilled water has a specific gravity of 1.000. Therefore, liquids heavier than water are scaled above 1.000 SG and those lighter than water are scaled below 1.000 SG.

How to Use and Read a Hydrometer: Function, Scale Types, and Use

A hydrometer is a device made up of a thin tube made from glass or plastic that is sealed at both ends. The scale to which the hydrometer is calibrated is either graduated or printed on the tube. One end of the tube is bulb-shaped and weighted with a ballast of either fine lead shot or steel shot. The ballast is what makes the instrument float upright in a liquid like a fishing bobber. A second glass or plastic cylinder, commonly known as a hydrometer jar, is filled with the liquid being measured. The hydrometer is then placed in the hydrometer jar containing the sample liquid.

The specific gravity of the sample liquid is indicated when the level of the sample liquid in the jar aligns with a point on the hydrometer scale. Depending on which scale is used, the number of times heavier or lighter than water the sample liquid weighs can now be recorded. In addition to reading specific gravity values, scales on a hydrometer can be calibrated to Baume, Brix, Alcohol, API (American Petroleum Institute Index) and others for specific chemicals.

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Brix Scale: A hydrometer calibrated to read in degrees of Brix or Balling, or percent of pure sucrose (sugar) by weight.

Baume Scale:A hydrometer calibrated to read degrees of Baume, which is a pair of scales: one for liquids heavier than water and one for liquids lighter than water.

Alcohol Scale: A standard specific gravity hydrometer used to measure specific gravity before and after a liquid ferments. The difference between the two specific gravity readings is referenced to an alcohol scale to determine percent alcohol by weight

API Scale: The API scale is a measure of how light or heavy a petroleum-based liquid is compared to water. It was designed to allow a comparison between the densities of petroleum liquids.

How to Use and Read a Hydrometer: Method of Reading

It is possible for some hydrometers to have multiple scales printed on them. It would be best if you filled the hydrometer jar with the sample liquid to use it. Place the device in the jar and twirl it to dislodge any trapped air. You can read from your desired scale once the hydrometer has settled. Note that you need to keep the sample liquid temperature at 60°F to get an accurate measurement. Evidently, you need to adjust the measurement for liquid temperatures other than 60°F.

For a standard hydrometer that is calibrated for 60ºF, you can use the following table for temperature adjustment. You need to find the temperature of the liquid in either column 1 or column 2 and add the corresponding value in column 3 to your specific gravity reading.

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Also note that for reading transparent liquids, the eyes should be placed slightly below the plane of the liquid surface and then raised slowly until this elliptic surface is seen as a straight line. The point at which the line sits on the hydrometer scale is recorded as the reading of the hydrometer.

There are times when the liquid is not sufficiently clear to read the hydrometer the way described above. In this case, you need to read from above the surface and try to estimate as accurately as possible the point at which the liquid rises on the hydrometer.

How to Use and Read a Hydrometer: Accuracy

Three factors are mainly responsible for the accuracy of measurement:

  1. Cleanliness: It is very important for the liquid to uniformly rise to merge into an almost invisible film on the stem. Therefore, the hydrometer surface, stem, hydrometer jar, and the liquid in which the readings are taken should be properly cleaned.
  2. Temperature: In order to avoid changes in density during testing, the hydrometer and liquid should be at the same temperature as the ambient temperature.
  3. Proper immersion: a hydrometer jar should have an inside diameter of approximately 1 inch (25mm) greater than the outside diameter of the hydrometer.

How to Use and Read a Hydrometer: The Steps

The first thing to do is to check the hydrometer’s temperature calibration. Since liquids expand and contract in response to temperature alterations, you need to test liquids at the temperature for which your hydrometer is designed so that you would get an accurate reading. This design temperature of the hydrometer should be listed on its instruction manual or label.

The second step to take is to measure the temperature of the liquid. Note whether it is more than some degree or too off from the hydrometer’s intended temperature. You might be able to correct your reading using the table provided for temperature adjustment a little earlier in the article.

Third, you shall pour a sample of the liquid into a clean container such as a transparent jar. Note that it should be large enough for the hydrometer to float in without hitting the sides or reaching its bottom.

You are now ready to lower down the hydrometer into the liquid just below the point at which it would naturally float. Make sure it is dry before inserting the hydrometer and also the hydrometer bulb does not touch the sides of bottom of the container as it settles in the liquid.

Now, you need to spin the hydrometer gently to release the air bubbles clinging onto the device. You cannot take your reading now and must wait until all bubbles are gone and the hydrometer and the liquid have stopped moving.

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You can now read the hydrometer scale at the lowest point of the liquid’s surface. This is because some of the liquid will cling onto the surface of the hydrometer stem due to capillary action in a way the makes a curved surface of the liquid. The vertex of this curve is where the reading shall be taken.

It is important to understand the scale of measurement after you take the reading. As stated earlier, there are several scales available for hydrometers, most common which is “specific gravity”.

How to Use and Read a Hydrometer: Commonly Asked Questions

  • How do I select the correct hydrometer for my needs?

Anyone using a hydrometer needs to have a general idea of the scale they need and the anticipated value on that scale for the process they are doing. Researching the industry norms for the process either online or via industry contacts can help you make the correct selection.

  • How do I convert degrees Baume (salt scale) to a specific gravity reading?

At 60°F, specific gravity can be calculated by using the following formulas:
Liquids lighter than water:
specific gravity = 140 / (degrees Baume + 130)

Liquids heavier than water:
specific gravity = 145 / (145 degrees Baume)

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How to Use and Read a Hydrometer: Ultimate Guide | Linquip (2024)


How do you read a hydrometer reading? ›

Actually Reading Your Hydrometer. You place the hydrometer inside the liquid, and it will start to oscillate for a moment before stopping. Make sure the hydrometer does not stick to the sides of the glass. When you finish, it will indicate that you have taken all the liquid you can at that density and temperature.

How do you read density using a hydrometer? ›

The liquid to test is poured into a tall container, often a graduated cylinder, and the hydrometer is gently lowered into the liquid until it floats freely. The point at which the surface of the liquid touches the stem of the hydrometer correlates to relative density.

What does 1.000 mean on a hydrometer? ›

In the standard hydrometer scale, known as the specific gravity scale, distilled water equals 1.000, the initial point of measurement. Liquids lighter than water are scaled below 1.000 specific gravity, and liquids heavier than water are scaled above 1.000 specific gravity.

What do the numbers mean on a hydrometer? ›

The more sugar in the liquid, the higher the reading. The more alcohol there is in the liquid the lower the reading (that is after fermentation as the sugar has now been converted into alcohol). For example, if the hydrometer is placed water at 20°C, it will read 1.000.

How do you measure the results of the hydrometer? ›

Insert the hydrometer in the measuring cylinder containing about 700 ml of water. Take the readings of the hydrometer at the top and bottom of the meniscus. The difference between two readings is taken as meniscus correction (Cm) which is a constant for a hydrometer.

What are the 3 scales found in a hydrometer? ›

The Triple Scale Hydrometer is the basic tool used by brewers and vintners worldwide for measuring sugar content, gravity and potential alcohol. The three scales used are specific gravity, Brix and potential alcohol. Simply float this in a sample of liquid and read where the liquid line meets the hydrometer.

How do you check alcohol content with a hydrometer? ›

What to Do: Measuring and Calculating Alcohol Using a Hydrometer
  1. Measure out about a cup of wort (or finished beer).
  2. Fill the hydrometer tube up to about 2 inches from the top.
  3. Insert the hydrometer. ...
  4. Look where the liquid intersects the markings on the hydrometer. ...
  5. Record the gravity reading.
Oct 5, 2022

What does the reading 1.025 indicate in hydrometer? ›

A seawater relative density reading of 1.025 on the load line hydrometer means that the seawater has an actual density of 1.025 x 0.9991kg/l = 1.0241kg/l. A one litre sample of seawater of this density will weigh 1.0241 kg in a vacuum.

What should a hydrometer read in water? ›

If your hydrometer is properly calibrated, it should read 1.000 when floating in pure water. Because the density of water changes with temperature, hydrometers are meant to be used at a specific temperature (either 60 °F/16 °C or 68 °F/20 °C).

Is a hydrometer supposed to float? ›

Hydrometer Jar Not Being Used: One of the requirements for taking a starting hydrometer reading, is the hydrometer needs to be able to float. If the container being used to hold the sample isn't tall enough, the hydrometer will sit on the bottom. Again, this will give you a wrong reading.

What does 40 on a hydrometer mean? ›

40 is the first number you can see above the liquid level; each line below the 40 is two gravity points. When reading the hydrometer, you have to ignore the "meniscus," that little bit of liquid that "curves" up the side of the hydrometer, and look at the actual fluid level. (

How much alcohol will a pound of sugar make? ›

Assuming you add enough grains to craft a 6.3% ABV beer, according to the chart, you'll need to add at least 1lb of sugar to hit a potential alcohol of 7.5%, because adding 1lb of sugar will increase the potential alcohol by 1.2% for a 5 gallon batch.

How do you know when fermentation is complete with a hydrometer? ›

To do so, take a hydrometer reading and then wait at least 24 hours before taking another reading. If the second reading is lower than the first, then fermentation is not yet complete. If the reading remains stagnant, then fermentation is complete and you can move on to the next step in the process.

What the hydrometer measures and in what units? ›

hydrometer, device for measuring some characteristics of a liquid, such as its density (weight per unit volume) or specific gravity (weight per unit volume compared with water).

What are the units of a hydrometer? ›

The hydrometer is considered to be an instrument to measure liquid density, marked in units of g/cm3, but corrections for other hydrometer scales can be determined as well.

What units does a hydrometer read in? ›

Brix Scale: A hydrometer calibrated to read in degrees of Brix or Balling, or percent of pure sucrose (sugar) by weight. Baume Scale: A hydrometer calibrated to read degrees of Baume, which is a pair of scales: one for liquids heavier than water and one for liquids lighter than water.

How does the hydrometer method work? ›

The hydrometer method of particle size analysis calculates the physical proportions of these soil particles based on their settling rates in an aqueous solution and identifies three size classes: sand (2000 – 50 µm), silt (50 – 2.0 µm) and clay < 2.0 µm.

What will be the reading when the hydrometer is dipped? ›

The reading when the hydrometer is dipped in water is 1.

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What does 10 mean on a hydrometer? ›

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.

What is the difference between a hygrometer and a hydrometer? ›

Do you know the difference between a hygrometer and a hydrometer? A hygrometer measures humidity, the amount of water vapour in air. A hydrometer, on the other hand, measures the density or specific gravity (SG) of a liquid by floating in the liquid.

What are the 2 types of hydrometers? ›

Types of Hydrometers

Lactometers: Lactometers or galactometers are measuring tools used to assess milk quality. Note that these instruments have a range of 1.025 to 1.035 g/ml. Saccharometers: Saccharometers measure the amount of sugar in a substance and are widely used in the brewery.

How do you calculate alcohol level? ›

It is calculated in grams per 100 mL of blood, so a BAC of 0.08 means your blood is 0.08% alcohol by volume. Using a breathalyzer, BAC is measured as grams per 210 Liters of breath (since the ratio of breath alcohol to blood alcohol is 2,100:1).

What specific gravity for moonshine mash? ›

Measure the specific gravity of the mash after the airlock slows down and you're not getting much activity. If the reading is at 1.000 or less, it is definitely done. If it's 1.020 or higher, you may want to wait a day or two and then take another reading.

Is ABV the same as alcohol percentage? ›

Sometimes you'll see both the ABV and “Proof” on the label of a bottle of liquors like vodka. The two measures indicate the percentage of alcohol in the liquid. The proof of the liquor is exactly double that of the ABV. For example, 80 proof vodka is equal to 40% alcohol, and 110 proof vodka is equal to 55% alcohol.

How accurate is alcohol hydrometer? ›

The process takes only a few minutes to carry out and an accuracy of about ±0.5% alcohol can be obtained using reasonable care in ensuring that both readings are made at the same temperature.

When a hydrometer is dipped in a liquid the reading is found to be 1.25 What is the density of the liquid? ›

=1. 25×1000=1250kg/m3.

What is the difference between 151h and 152h hydrometer? ›

The 151h hydrometer reads the specific gravity of the suspension and has a capacity of about 45g of dry soil in the 1,000ml liquid solution. The 152h hydrometer measures the grams per liter of the suspension with a capacity of up to 55g of dry soil in the 1,000ml liquid solution.

How long does it take for a hydrometer to get an accurate reading? ›

Dampen a towel (not dripping wet, but good and damp), then wrap the hygrometer in the towel for 30 to 45 minutes. Then unwrap it and read the humidity (quickly). If your hygrometer is perfectly calibrated (few are) it will be reading exactly 100% humidity. Most likely, it will be reading somewhere between 80 and 90%.

How can I make my hydrometer more accurate? ›


The hydrometer and liquid should be at the temperature of the surrounding atmosphere to prevent changes in density during the testing. To ensure uniformity of density and temperature, the liquid should be completely stirred shortly before the observation is made.

What does it mean if hydrometer sinks to bottom? ›

Distilling or proofing hydrometers essentially do the same thing as brewing hydrometers. They tell the distiller how much alcohol is in a solution. However, the density of spirits and fuel alcohol is so low that a brewing hydrometer would sink right to the bottom. This is because alcohol is less dense than water.

What does it mean if hydrometer sinks? ›

If a fluid is less dense, the hydrometer will need to displace more fluid to reach the balancing point between upward and downward force, so it sinks deeper into the fluid. If the fluid is more dense, such as the salt-water solution, the volume the hydrometer needs to displace will be less, so it floats higher.

How do you adjust a hydrometer? ›

If your hygrometer is reading below or above 75%, you will need to adjust the reading to register 75%. For most analog hygrometers, simply adjust the needle to read 75% on the gauge by turning the screw on the back of the hygrometer with a small screwdriver. Many digital hygrometers can be adjusted with a button.

What is the starting gravity for moonshine? ›

Alcohol has a starting gravity (SG) of 1.000 on the hydrometer scale. Temperature will also play a role in the hydrometer reading.It is important to ensure your hydrometer is calibrated to a standard reading temperature is 70°F or 20°C.

What sugar is best for moonshine? ›

Simple sugars are the easiest for yeast to consume because they are 100% fermentable. Fructose, or Fruit Sugar, is found to be the sweetest part of sugars and is a simple sugar that can be found in honey, fruit, and many root vegetables.

What is the best sugar for making alcohol? ›

Pure sucrose is the reference standard for all fermentable sugars because it contributes 100% of its weight as fermentable extract.

Does more sugar mean stronger alcohol? ›

If there is more available sugar, the yeast has more food to eat, which produces more alcohol. Sometimes brewers opt to add different types of sugar – for example, brown sugar, dextrose, honey or palm sugar – to increase the alcohol content and change the flavor of a beer.

How do I know my ferment is ready? ›

Within 1 week it should start to taste sour. If you like it, it is done. If not let it continue to ferment.

How do I know if my fermentation is stuck? ›

You can catch a stalling fermentation within the first 24 hours by noticing that your pH levels aren't falling rapidly. Because beer doesn't ferment at a constant rate, after this one-day window you shouldn't worry until the gravity reading has stagnated for at least 48-to-72 hours.

How do you know if fermentation is successful? ›


The lactic acid fermentation process produces lactic acid bacteria that create gases when they feast on the vegetables. These gases are often visible as bubbles throughout the jar after a few days at room temperature and are a good sign.

How do you calculate alcohol with a hydrometer? ›

Your percent alcohol can be given by the formula: ABV(%) = (Initial Gravity - Final Gravity) * 131.25. So if your initial gravity was 1.108, and your final gravity was 1.041, your beer is approximately 8.79% alcohol by volume. Once again, this is only an approximation, and loses accuracy as the alcohol content goes up.

What does 40 mean on a hydrometer? ›

40 is the first number you can see above the liquid level; each line below the 40 is two gravity points. When reading the hydrometer, you have to ignore the "meniscus," that little bit of liquid that "curves" up the side of the hydrometer, and look at the actual fluid level. (

Can a hydrometer be wrong? ›

If the container being used to hold the sample isn't tall enough, the hydrometer will sit on the bottom. Again, this will give you a wrong reading. This normally happens when the winemaker is trying to use the plastic tube the hydrometer came in to take the reading.

What is the range for alcohol on a hydrometer? ›

On most hydrometers, the Potential Alcohol scale ranges from 0-20% alcohol.

How do you calculate alcohol content in liquor? ›

You can work out how many units there are in any drink by multiplying the total volume of a drink (in ml) by its ABV (measured as a percentage) and dividing the result by 1,000.

How do you calculate grams of alcohol? ›

Find the alcohol dose.
  1. You can also find the alcohol dose using the formula: (Volume of drinks) x (AC of drinks) x 0.789 = grams of alcohol consumed.
  2. If your area has a different alcohol content in a standard drink, you will need to multiply the number of standard drinks consumed by that alcohol content in grams.

What is the easiest way to measure alcohol content? ›

A hydrometer is a tubelike instrument brewers can use to help calculate the alcohol by volume (ABV) percentage of their beers. An alternative to using the hydrometer is a refractometer, another simple instrument that can be used to measure concentration of substances dissolved in a liquid.

What if my hydrometer reading is too high? ›

If the hydrometer reading is 1.000, your instrument is correctly calibrated. If it is too high, you can use a file to shave off some of the glass from the bottom of the hydrometer until it hits 1.000.

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