How to Use a Hydrometer in 4 Easy Steps

Crafting the perfect brew at home requires imagination and attention to detail. Knowing how to use a hydrometer can help you make sure your beer comes out exactly how you expect.

What Is a Hydrometer?

A hydrometer is a basic tool used to measure the ratio of a sample liquid’s density to the density of water. When it comes to brewing beer, a hydrometer is necessary to show you the degree to which the yeast is converting sugar into ethanol, ultimately helping you gauge the health and success of the fermentation of your beer.

Why Do I Need a Hydrometer to Make Beer?

Home brewing is a delicate process. A lot of time and effort goes into it, and there are many opportunities for things to go wrong. Perhaps the most important stage within beer making is fermentation.

This particular stage of the brewing process is what makes the hydrometer so important, as it is the device that gives you insight on how the fermentation process is going. A hydrometer can be the single tool that alerts you of issues during fermentation, allowing you to make adjustments as needed.

How Do I Use a Hydrometer?

Using a hydrometer isn’t as complicated as some might think. It really comes down to a simple four-step process:

1. Retrieve Sample and Insert Hydrometer

You will need to take your first measurement after the cool-down, before pitching the yeast. The reading that you will get is called the original gravity, often referred to as “OG.”

To obtain this reading, first use a beer thief to retrieve a sample of the wort and transfer it to a testing jar or cylinder. The testing container should have enough liquid in it to fully suspend the hydrometer.

After transferring a sample to your test container, place the hydrometer in the wort and allow it to buoy. Wait until all air has escaped from the liquid or gravitated upward. From there, center and vertically position your hydrometer so it can depict the most accurate reading.

2. Obtain the Original Gravity Reading

The increments of your hydrometer represent specific gravity points. The level to which the liquid rises is where your gravity reading should occur (we’ll call this the liquid-air line).

At this point, record the number on your hydrometer that is being crossed by the liquid-air line. A typical wort OG will be between 1.035 and 1.060. Your ingredient kit will list an OG so that you’ll have a reference for what your wort’s OG should be close to.

Note: To get the most accurate data, read the bottom of the meniscus—this is where the liquid is level and not pulled by tension up the sides of the container or hydrometer itself.

3. Calculate with Temperature

Hydrometer readings are stated assuming a standard temperature of 15°C (59°F), so knowing the temperature of your wort is crucial for an accurate reading. If your temperature reading is different, be sure to calibrate.

Calculate the difference by using the table below. Simply add the “△ Gravity” to your initial reading to obtain the correct specific gravity.

4. Repeat to Obtain Final Gravity Reading

You’ll want to take another hydrometer reading when the fermentation process is complete or nearing its end. And congratulations—now that your brew has an alcoholic content, it is officially beer and no longer wort.

This reading will be the final gravity, or “FG,” and should be close to the listed FG included in your ingredient kit instructions. To give you a good idea of what to look for, a typical beer’s FG is between 1.015 and 1.005 and should be about 1/4 or 1/5 of the beer’s OG.

Avoid a Common Hydrometer Mistake

A lot of beginners make the mistake of testing their brew too often. Remember that each time you test, you run the risk of exposing your beer to harmful air or bacteria that could ruin an entire batch.

We recommend only testing once before pitching and once after fermentation is believed to be complete. If additional testing is needed, perhaps due to stuck fermentation, do your best to use extreme caution.