Measuring Alcohol Content: How to use a Hydrometer

Measuring Alcohol Content

One of the first upgrades you are going to want to make to your brewing process is to start measuring the alcohol content. You can usually estimate within a few percentage points based on the type of alcohol you are brewing – for example our beginner’s wine comes out to around 8-12% – but with a couple cheap tools and some simple calculations you can make a much more precise measurement of your brew’s ABV. Not only will this make you feel more professional, but you’ll actually know how much alcohol you are drinking.

Tools of the trade

The hydrometer (sometimes called a saccharometer) is the simplest tool for measuring alcohol content, and our recommended method. It measures alcohol content by comparing the relative density of your brew to that of distilled water.

Another alternative is the refractometer, which measures alcohol by measuring how light is bent through the liquid. Most professionals use refractometers because it only requires a few drops, but they are usually more expensive, require more complicated calculation, and need to be calibrated before use. Check out our upcoming refractometer guide to learn more.

The Science

A hydrometer works by comparing the relative density, or specific gravity, of a liquid to that of distilled water. The basic components of a hydrometer are a tube meant to hold the liquid and a glass rod with one bulbous end and one long skinny end.

The bulbous end is weighted to make the hydrometer float upright, while the long skinny end has markings similar to a thermometer. These markings let you measure the specific gravity of a liquid. The more dense the liquid, the higher the hydrometer will float. Hydrometers are calibrated so that distilled water will give you a reading of 1.000.

When buying a hydrometer online, make sure you are buying a kit that includes a test cylinder and is calibrated to be accurate at the lower alcohol ranges that include beer and wine. Our favorite can be found on amazon for around 12 dollars:

Home Brew Ohio 6839-5068 Triple Scale Hydrometer and Test Jar Combo

Now how does this help home brewers? Yeast converts sugar into alcohol. Sugar is more dense than water, and changes the specific gravity of your brew. Similarly, alcohol is less dense than water, which moves the specific gravity in the opposite direction. By measuring the specific gravity before (Original Gravity) and after fermentation  (Final Gravity), you can calculate how much sugar has been changed into alcohol.

How to Use a Hydrometer

You will need the hydrometer itself, including the tube, and a method of removing some of the liquid from your fermentation vessel. You can invest in a wine thief, but any sort of pipette, ladle or turkey baster will do. As a last resort, you can pour your brew into the vessel but this is not recommended as it disturbs the sediment on the bottom.

Before using the hydrometer, you may want to make sure it is calibrated by testing it in distilled water. The hydrometer should float such that the 1.000 mark lines up with the water level measured at the bottom of the meniscus

Do not worry about sanitizing the hydrometer, as the liquid used to measure ABV should not be poured back into your fermentation vessel.

1. Using your wine thief or ladle, fill up the hydrometer tube roughly 3/4 of the way to the top.

2. Slowly lower the hydrometer into the tube to avoid a splash. Spin the hydrometer to release any bubbles that may have formed underneath. Make sure the hydrometer is floating freely and not resting against the side of the hydrometer.

3. Take a reading from the bottom of the meniscus of the water. Record this reading. This is your original gravity.


4. After fermentation is done, repeat the same steps to get a final gravity reading.

5. Calculate your ABV. One commonly accepted simple formula is:

(OG – FG) x 131.25 = ABV %

FG : Final Gravity
OG: Original Gravity
ABV: Alcohol by Volume

That’s it! Now you have an easy and inexpensive way to calculate how much alcohol you’ve made.


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