Mead Hydrometer Guide: OG, FG, ABV and Safe Bottling

A hydrometer is the most useful safety and record-keeping tool in a beginner mead kit. It measures specific gravity: the density of a liquid compared with water.

As yeast consumes sugar, gravity normally falls. Comparing readings tells you far more than counting bubbles—and helps prevent bottling a mead that is still fermenting.

What OG and FG mean

• Original gravity (OG): the reading after honey and water are mixed, before fermentation.
• Final gravity (FG): the stable reading after fermentation has ended.
• Specific gravity (SG): any gravity reading, whether taken at the start, middle or end.

Pure water reads approximately 1.000 at the hydrometer’s calibration temperature. A honey-rich must might begin around 1.090–1.120. A dry fermented mead can finish below 1.000 because alcohol is less dense than water.

Gravity does not map perfectly to perceived sweetness. Acidity, tannin, alcohol and aroma all change how sweet the same FG tastes.

How to take a reading

1. Check calibration. Read the hydrometer’s instructions and calibration temperature, commonly 20°C or 15.6°C. Test it in water at that temperature; it should be close to 1.000.
2. Clean and sanitise. Treat the trial jar, sample tool and anything else that may contact the mead.
3. Remove a sample. Take enough liquid for the hydrometer to float without touching the bottom.
4. Release bubbles. Lower the hydrometer gently and spin it. Carbon-dioxide bubbles stuck to the stem can lift it and distort the result.
5. Read at eye level. Follow the instrument’s directions for the meniscus, normally reading at the bottom of the liquid’s curved surface.
6. Record gravity and temperature. Also note the date, batch and how the mead looks and smells.
7. Do not pour the sample back. Taste it or discard it to avoid introducing contamination.

Temperature changes liquid density. If your sample is far from calibration temperature, use the correction table supplied with the hydrometer or a reputable calculator. Cooling the sample near the calibration temperature is usually simplest.

Estimating alcohol by volume

A common homebrew approximation is:

ABV ≈ (OG − FG) × 131.25

Example:

• OG: 1.100
• FG: 1.000
• Difference: 0.100
• Estimated ABV: 0.100 × 131.25 = 13.1%

This is an estimate. It assumes accurate readings and is less exact for unusual or very strong fermentations. Without an actual OG reading, the recipe’s predicted OG can only give you a rough result.

How to confirm fermentation has finished

An airlock cannot confirm completion. It can stop because the lid leaks, and it can bubble because temperature or air pressure changes.

Instead:

1. Take a reading when active fermentation appears to have subsided.
2. Wait several days; for a new mead maker, a week is a cautious interval.
3. Take a second reading under similar conditions.
4. If the number has fallen, fermentation is continuing—wait and test again.
5. If readings match, assess whether the value is plausible for the recipe and yeast before packaging.

Stable gravity is necessary before bottling, but context matters. A batch stuck at 1.060 for a week has not necessarily completed successfully; it may need fermentation troubleshooting.

Reading the scale correctly

Hydrometer scales vary. On a specific-gravity scale:

• each numbered step may represent 0.010;
• smaller marks often represent 0.001 or 0.002;
• values decrease as fermentation progresses.

Do not confuse specific gravity with Brix, Balling or potential-alcohol scales printed on the same instrument. Use one scale consistently in your notes.

Common errors

Reading foam instead of liquid

Move foam aside or use a clean sample. The actual liquid surface is what matters.

Bubbles attached to the hydrometer

Spin the instrument gently. If the sample is highly carbonated, let it release gas without exposing the main batch.

The hydrometer touches the jar

Use a wider or fuller trial jar so it floats freely.

Forgetting temperature

A warm sample can read differently from a cool one. Record temperature and correct when required.

Using a refractometer after fermentation without correction

Alcohol changes refractometer readings. A raw post-fermentation Brix reading is not equivalent to a hydrometer FG; it needs an alcohol correction based on the original reading.

Assuming a target FG is guaranteed

Recipe numbers are predictions. Honey composition, yeast health and fermentation conditions vary. Look for a stable, plausible result rather than forcing the mead to hit one exact number.

Bottling safety

Never bottle because a certain number of days has elapsed. Never assume that clear mead, settled sediment or a silent airlock means it is finished.

For still mead:

• confirm stable gravity across repeated readings;
• do not add honey or priming sugar at bottling;
• use sound bottles and compatible closures;
• if gravity resumes falling, delay packaging.

Carbonated mead requires additional calculations, pressure-rated bottles and controlled priming. The beginner recipe deliberately makes still mead.

Simple batch record

Your figures will differ; this table demonstrates the process, not a required target.

Continue learning

• Beginner’s 4.5-litre mead recipe
• Mead-making equipment checklist
• Fermentation troubleshooting

Further reading: American Homebrewers Association—How to Take an Accurate Hydrometer Reading.

Reviewed 11 October 2026.