How to Use a Hydrometer

The hydrometer is the home winemaker's most important tool. It tells you how much sugar is in your must, how well fermentation is progressing, and ultimately how much alcohol your wine contains. Once you understand it, you'll wonder how anyone makes wine without one.

What is Specific Gravity?

Specific gravity (SG) is a measure of density relative to water. Pure water has an SG of 1.000. Dissolve sugar in it and the SG rises — to around 1.040 for a light wine starting gravity, or 1.090 for something stronger. As yeast converts sugar to alcohol, the SG drops back towards (and sometimes below) 1.000.

Taking a Reading

• 1.Pour a sample of your must or wine into the trial jar — enough to float the hydrometer
• 2.Lower the hydrometer gently into the liquid
• 3.Give it a gentle spin to dislodge any bubbles
• 4.Read the scale where the liquid surface crosses the hydrometer — at eye level
• 5.Record the reading

What the Numbers Mean

• 1.080–1.090 — Good starting gravity for a standard country wine, around 12% potential ABV
• 1.040–1.060 — Too low to start — add more sugar
• 1.000 — Fermentation has finished (bone dry)
• Below 1.000 — Very dry, strong wine. Normal for high-gravity starts

Calculating ABV

The simple formula: (OG − FG) × 131.25 = ABV

So if you started at 1.090 and finished at 0.996:

(1.090 − 0.996) × 131.25 = 12.3% ABV

Use our ABV calculator to do this automatically.

Temperature Correction

Hydrometers are calibrated at 20°C. If your must is warmer or cooler, your reading will be slightly off. Use our Hydrometer Temperature Correction calculator to get an accurate reading at any temperature.

When to Take Readings

• Before adding yeast — this is your Original Gravity (OG)
• Every few days during fermentation — to track progress
• When bubbling stops — to confirm fermentation is complete
• Two readings 48 hours apart showing the same number — fermentation is done

Common Mistakes

Reading from above — always read at eye level, not looking down

Not spinning the hydrometer — bubbles clinging to the glass will give a false reading

Measuring at high temperatures — wait until your must has cooled to near room temperature

Ready to start brewing?

Track your brews, log readings, and get AI advice from Vinnie.

Related Guides