How to Measure Alcohol With a Hydrometer
A Simple Guide to Tracking Fermentation and Calculating ABV
If you want consistent results in your brewing, you need control.
Control starts with measurement.
A hydrometer is one of the most important tools in your brewing kit. Whether you’re making beer, cider or a sugar wash, it tells you exactly what is happening during fermentation and how much alcohol you have produced.
No guessing. No assumptions. Just proper brewing.
What Is a Hydrometer?
A Simple Guide to Tracking Fermentation and Calculating ABV
If you want consistent results in your brewing, you need control.
Control starts with measurement.
A hydrometer is one of the most important tools in your brewing kit. Whether you’re making beer, cider or a sugar wash, it tells you exactly what is happening during fermentation and how much alcohol you have produced.
No guessing. No assumptions. Just proper brewing.
What Is a Hydrometer?
A hydrometer measures specific gravity which is the density of your liquid compared to water.
Before fermentation your wort contains sugar which makes it heavier.
After fermentation yeast converts that sugar into alcohol which is lighter.
By measuring the change in density, you can calculate your alcohol percentage.
Simple science. Big impact.
Why This Matters
Using a hydrometer allows you to:
• Track fermentation progress
• Confirm fermentation is finished
• Calculate ABV accurately
• Improve recipe consistency
• Avoid bottling too early and creating bottle bombs
If you are serious about brewing better beer, this tool is essential.
Step 1: Take Your Original Gravity (OG)
Before pitching yeast:
• Fill a sanitised test jar with wort
• Gently lower the hydrometer into the sample
• Take the reading at eye level
This number is your Original Gravity.
Example: 1.050
Always take your OG after chilling and before pitching yeast for the most accurate reading.
Step 2: Take Your Final Gravity (FG)
Once fermentation appears complete, take another reading.
To confirm fermentation has finished properly:
• Take a reading
• Wait 2 to 3 days
• Take another reading
If the gravity remains the same, fermentation is complete.
Example: 1.010
Step 3: Calculate Your ABV
Use this simple formula:
ABV (%) = (OG − FG) × 131.25
Example calculation:
(1.050 − 1.010) × 131.25 = 5.25 % ABV
That is your finished alcohol percentage.
Brewcraft Pro Tips
• Always sanitise your hydrometer and test jar
• Spin the hydrometer gently to remove bubbles
• Read at the calibration temperature which is usually 20 °C
• Never pour the sample back into your fermenter
• Keep detailed notes for every batch
Consistency separates average brewers from great brewers.
Common Mistakes to Avoid
• Taking a reading while fermentation is still active
• Not accounting for temperature differences
• Letting CO₂ bubbles cling to the hydrometer
• Returning contaminated samples to the fermenter
Small mistakes can affect your final numbers.
Equipment Makes It Easier
A quality hydrometer and proper test jar make the process simple and accurate.
If you are using a Grainfather system, accurate temperature control makes your gravity readings even more reliable and repeatable.
Good equipment does not replace skill, but it does make precision easier.
Final Takeaway
Brewing consistently good beer is not about luck.
It is about measurement, control and repeatability.
A hydrometer gives you that control and helps you brew better every time.