How to Read a Hydrometer

by Karl S | Updated: October 24, 2021

The hydrometer is an instrument for measuring the density, velocity and gravity of liquid elements.

A hydrometer is an instrument developed on the same basis as Archimedes’ theory for estimating the gold crown; it’s also known as the Archimedes Principle.

The instrument is a glass rod; what makes this rod especial is that it comes with a little mercury and lead inside. The metal inside the bar allows it to float in the liquid without sinking.

Another element is the paper glued to the bar, which allows to take the readings. 

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Why should you learn how to read a hydrometer?

The hydrometer, as mentioned above, is used to measure the density of water and the elements suspended in it. To understand its importance, you only need to know its use.

The hydrometer can record the concentration and saturation of elements in the water. For instance, we can find the levels of salt contained in the water or how much or the gravity of a liquid, like beer. Let’s get into it.

What is the temperature?

The first thing you should know is the temperature of the liquid. It is necessary for calibrating the hydrometer to that temperature. The second thing you should do before taking a reading is to clean the instrument to avoid external elements.

To clean it, you should use a clean cotton towel, helping to place a soapy solution. Gently run the sheet through the hydrometer, avoiding scratching or breaking it during the process.

To use the hydrometer is simple; you only need to place the instrument inside the liquid. The hydrometer will oscillate until it stops, and you will be able to take the measurement marked by the device. 

The Applications

The application of the above case applies mainly in aquariums. The hydrometer allows determining the levels of salt in the water for the fish, for establishing a suitable habitat. The hydrometer also records the levels of sand and marine elements contained in it.

Another application for measuring salt is in the kitchen. Chefs often use this tool to prevent food from becoming salty. It is a way to avoid 100% of the food from being over-salted. 

As you can see, a hydrometer is useful for measuring salt concentration in water. It is not hard to see how it becomes useful for brewers. The amount of salt floating around your water can change the flavor and overall feel of whatever you brew. However, if you are aware of the salt content of the water, you can investigate how it is best to proceed.

So far, it is easy to conclude that hydrometers are an important tool for many brewers. However, measuring salt content is not the only use for this handy companion. There are more uses that maybe you cannot think of.

Another element that measures is sugar in liquid components. The application varies depending on the manufacturing context. Juices, chocolate drinks, soft drinks, among others, measure the amount of sugar with the hydrometer. The hydrometer allows establishing the quantity of each element within the liquor for legal reasons.

Therefore, another use is measuring the amount of sugar in alcoholic beverages. When it comes to that, there are more factors that you can measure with the hydrometer. The first is the amount of sugar contained in the drink in question. The amount of sugar is one of the factors that will determine the alcohol volume in your brew.

Another factor for alcoholic beverages is the fermentation of sugars within the liquid. Regarding sugar, the more it ferments, the stronger the taste and the loss of alcohol. An example is whiskey: the less it ages, the higher the alcohol content and the less defined taste.

Beer is another case in which a hydrometer is vital. The application varies depending on the aspects of the recipe. The first application is the same as with whiskey and other brews. It’s necessary for measuring the grade of sugar fermentation within the beer; this helps to obtain different styles of beer with diverse tastes, notes, and alcohol volume.

The hydrometer can record the density of other elements in the beer such as barley. Knowing the concentration of barley in beer is crucial; it is the ingredient that gives most of its flavor.

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. The measurement shows the amount of water introduced into the hydrometer.

There are certain myths and recommendations when taking a measurement that we will discuss and in some cases, correct. The first factor is relevant when making the measurement. There is a myth that says you should use the water peak that forms around the hydrometer. The correct way is to use the surface of the water as a reference.

A final gravity reading with my hydrometer; holding steady at 1.088.

There is another myth that releasing the hydrometer from a higher height is faster. Let me tell you something: what you can get by doing that is a broken hydrometer. The hydrometer is a delicate instrument, not a stone or a rocket for throwing it around. The hydrometer must be placed gently into the liquid.

The myth of turning the hydrometer into the water to make it more useful is erroneous. The hydrometer is not coin or wheel for you to spin. If you do it, you can cause a wrong measurement. Another thing you can produce is the capsule that surrounds the metal to break and damage the instrument.

Being a lazy person is a problem and even more so when you have to make precision measurements. Not cleaning the hydrometer when you have used it previously causes measurement errors. The reason is simple; you are introducing foreign particles into the study. The particles get impregnated in the instrument and cause errors.

In the case of industrial hydrometers, the measurement is automatic. The hydrometer always shows the density of the production batch. However, you must adjust them to the specifications. The specifications to consider are from both the machinery manufacturer and the production.

Regarding the manufacturer, it requires knowledge of the application and implementation manual, as well as compatibility with the machines. 

In production, the storage capacity of the cylinder and the temperature of the beverage are the most important elements. Another factor to consider is the type of ingredients used.

There are more sensitive hydrometers, and specific ingredients can give a false result. This measurement system is recommended especially for the production of new products and production lines. Guaranteeing an active production and with the desired characteristics.

As you can see, industrial hydrometers are more difficult to configure than normal ones due to their high complexity. Regardless, having them is worth it because it guarantees a successful production.  

How a Precision Hydrometer Made my Brewing More Enjoyable

I was kinda shocked when I read my original gravity reading -> 1.064. That was 4 points higher than my target and I had tracked the gravity throughout the boil with a refractometer. The gravity was right on track, so why the discrepancy when I gave the finished batch one final check with the hydrometer? A simple test gave me my answer.

I put the hydrometer in its jar and added distilled 60°F water. The reading was 1.004. The hydrometer’s calibration was off. “Dammit.”

So, on my next trip to the homebrew store I exchange it for a new one. I’m skeptical at this point. The first thing I do when I get home is test it in water -> 1.002. “Screw this.” After two lousy hydrometers in a row I decided to make a change. Enter the Lab Grade Precision Hydrometer.

It wasn’t just the calibration. I’ve always had a hard time reading the lines on a standard hydrometer. They are so close together it can give you a headache.

“Is that 1.012 or 1.014?”

I had heard of precision hydrometers and decided to give them a shot. I bought two:

It’s sort of annoying to have to buy two hydrometers, but that’s exactly why these are better: They don’t cram the entire gravity scale onto a single hydrometer.

Here, let me show you…

Here’s a picture of standard hydrometer:


Notice how close together the numbers are. Now here’s the same reading on a precision hydrometer:

Precision Hydrometer

Notice how much space is between 1.020 and 1.030. See how much easier to read it is?

It’s not only the ease of measurement that I enjoy. They are much more accurate too. You can bet I checked the calibration – spot on.

A side benefit is that I haven’t broken one yet. I’ve lost track, but I’m somewhere close to double digits in how many cheapo hydrometers I’ve broken in my brewing career. When you spend more on something you take better care of it.

Not everyone will find it worthwhile to spend $20 on a hydrometer. I know plenty of brewers who don’t measure their gravity at all. No problem with that.

But if you’re like me and you like being precise + accurate with readings, you might enjoy this. Or maybe you just want to give your eyes a break.

Either way, it’s been totally worth it.

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Brewer's Elite Hydrometer & Test Jar Combo

This specific gravity hydrometer allows you to easily calculate Alcohol % (ABV) - Graduated color bands help you know when you brew is ready, and larger fonts are so easy to read.

Check Price
03/16/2023 05:32 pm GMT

Getting a Hydrometer

The hydrometer as a measuring instrument is available in various versions. The hydrometer comes in the classic version with a crystalline tube and also in a digital version. Another version of the hydrometer is a more modern one, for production of products in large quantities such as beer. 

You can get the classic and digital hydrometers in any store selling chemistry tools. And of course, there are specifically designed tools just for homebrewers like this one I have

If you don’t want to pay for a hydrometer, you can make a homemade one. Let’s explain step by step how to build it with common materials and in a simple way. 

The materials that we are going to use can be obtained almost anywhere. The materials that we will use are a straw, a large jar of olives or capers. The final element is clay, something uniform.

The first thing is to grab the straw and check that it is not bent in any way. Place the clay  on one end of the straw. You must take care that it is covered; it cannot have any filtration since it will not float.

Place 100ml of water in the olive bottle, which would be equivalent to half a cup of water. When placing the water, place the straw with the blocked end facing upwards. After you put it, wait for it to stop oscillating and take the initial measurement and you will have the hydrometer calibrated. It is recommended to place a different coloured line for each measure.

If the straws do not float as it should, you can add a needle or any metallic material inside. The metal will add more weight, making the straw swim without a problem.

However, you may need something more large-scale; therefore, we are going to explain how to get an industrial instrument. The first factor to study is the type of product to be manufactured and the type of machinery to be used. An example is beer, which requires setting the amount you will produce.

The hydrometer must adjust to the machinery used for producing the beer. The hydrometer can be obtained at many construction stores. Ask for the type of hydrometer according to your machinery; you can buy the wrong one, and it will not function as it should. 

You need to calibrate the hydrometer for the temperature and pressure of the machine. Calibrating the heat is fundamental for a correct measurement. Temperature can affect the density of the liquid and, consequently, the effectiveness of the instrument.

Another factor to consider when acquiring the hydrometer is the manufacturer of your machinery. The manufacturer has precise specifications regarding the type of connectors; this is crucial for the hydrometer.

Industrial hydrometers are available in online stores. You can find them on sites like Amazon and eBay, from national and international distributors. Another option is in virtual stores from the same suppliers; you can get the specifications of the instrument and its compatibility.

In short, you can get the hydrometer both online or at a specialist store. You only need to make sure that know the specifications of the instrument before you buy it.

What if I skip it? 

The consequences of not using the hydrometer can vary depending on the situation. The vast majority are not good, so we always recommend its use. We advice using the hydrometer in the cases we are going to mention. Those that we don’t suggest but support in the process also use it.

Hydrometers are vital when producing any alcoholic beverage. If you don’t use it, you run the risk of killing your product. In addition, if you do not use the instrument, the other way to guarantee the quality of your results is by using a more time and production resources. The resources used range from personnel, other measuring instruments and their maintenance.

The use of these additional resources will cause an additional cost for production. Expenditure will increase as production and product diversity increases.

There are other consequences of not using the hydrometer to verify the sugar density within the product. The first one is a low amount of sugar in your distillate; this causes a lesser degree of alcohol content than desired. Low sugar will detract from the taste and quality of your drink.

A high amount of sugar, on the other hand, can cause a high degree of alcohol in the drink. The high high rate alcohol volume can cause the beverage to be dangerous when consumed. 

In several alcoholic beverages, the hydrometer registers the density of other elements. A significant example is—again—beer. Beer requires a specific density to give it a good taste. The wrong amount will provide it with a very loose or very strong feeling depending on the amount.

In wines, you need to know the density of the juice to understand how strong the taste is. In many cases, you need a very strong or very soft wine, depending on its use. Sweet wines are used for direct consumption, while intense wine works for cooking.

If you do not measure the amount of fruity taste of the wine, you run the risk that it will not fulfil its function.

When it comes to fermentation, the hydrometer still fulfils a fundamental role. The density of the dink shows the level of alcoholic fermentation. It is vital for the production of great aged whiskies.

In short, for the production of any alcoholic beverage, you can save both time and money by using this tool. If you decide to skip it, you run the risk of losing your product and gaining bad publicity for your brand. It’s already up to you what you prefer: to invest a little more or run the risk of losing a production batch.

The hydrometer is essential if you wish to sow the ingredients of your drinks by yourself. Planting requires an acceptable level of humidity, even barley—despite its resilience. One element to consider is the level of fertility of the soil; the hydrometer will show if soil work is necessary. Another use is that it verifies if the type of soil is suitable for what you want to grow.

If you don’t use the hydrometer, you can quickly lose all the work and resources you invested. Planting in unsuitable soil will cause the plants not to grow and the resources to be missed. It is preferable to use it to verify if it is possible to sow in a type of soil.

In the case of vineyards and plantations to produce drinks, it is vital. Plants are the raw material for making wines, beers and malt whiskies. Failure to use the hydrometer can significantly affect the production of fruits and plants for your product. Poor soil conditions can affect fruit development as well as taste.

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Fruits with little or strange flavour directly affect the taste of the beverage. The result will not have the desired character, and you will lose sales and customers by defects in the drink.

Frequently Asked Questions

What is a Hydrometer and Why is it Important in Brewing?

A hydrometer is an instrument used to measure the density, velocity, and gravity of liquid elements. It is particularly important in brewing as it can record the concentration and saturation of elements in the water, such as the levels of salt or the gravity of a liquid like beer. This information is crucial in determining the flavor and overall feel of the brew.

How Do You Use a Hydrometer?

To use a hydrometer, you first need to know the temperature of the liquid for calibration purposes. The instrument should be clean to avoid external elements. Once prepared, you simply place the hydrometer inside the liquid. It will oscillate until it stops, at which point you can take the measurement marked by the device.

What are Some Common Misconceptions About Using a Hydrometer?

Some common misconceptions include the idea that you should use the water peak that forms around the hydrometer for measurement (you should use the water surface as a reference), or that releasing the hydrometer from a higher height will speed up the process (this can actually break the hydrometer). It’s also incorrect to spin the hydrometer in the water, as this can cause inaccurate measurements.

What are the Applications of a Hydrometer?

The applications of a hydrometer are vast. It can be used in aquariums to determine the levels of salt in the water, in kitchens to prevent food from becoming too salty, and in the production of various beverages to measure the amount of sugar or other elements. In brewing, it’s used to measure the grade of sugar fermentation within the beer, which helps to obtain different styles of beer with diverse tastes, notes, and alcohol volume.

Can You Make a Homemade Hydrometer?

Yes, it’s possible to make a homemade hydrometer using common materials like a straw, a large jar, and clay. However, for large-scale brewing or more precise measurements, it’s recommended to use a professional hydrometer, which can be obtained online or at a specialist store.