Brew Gravity Calculator
Correct your hydrometer readings for temperature, then estimate ABV and attenuation from OG and FG.
Tip: If you only know OG, leave FG blank and calculate correction first.
What is brew gravity and why does it matter?
In brewing, gravity measures how dense your wort or beer is compared to water. This density is mostly driven by dissolved sugars. Original Gravity (OG) tells you how much fermentable sugar is present before yeast starts working. Final Gravity (FG) tells you how much sugar remains after fermentation. Together, these numbers help you predict alcohol, body, sweetness, and overall balance.
A brew gravity calculator simplifies the math so you can make better recipe decisions quickly. Instead of guessing whether your IPA finished too high or if your stout fermented enough, you can plug in readings and get useful answers in seconds.
How to use this brew gravity calculator
1) Enter your OG reading
Add the hydrometer reading you took before fermentation. Typical values range from about 1.035 for light beers up to 1.090+ for stronger styles.
2) Enter sample temperature and calibration temperature
Hydrometers are calibrated at a specific temperature (commonly 60°F or 68°F). If your sample is warmer or cooler than the calibration point, your reading needs correction. This tool automatically applies temperature correction using a standard polynomial equation.
3) Add FG to estimate ABV and attenuation
If you know your final gravity, the calculator will estimate alcohol by volume (ABV), apparent attenuation, and gravity points consumed. This helps you evaluate fermentation performance and compare batches.
Core brewing metrics explained
- Corrected OG: Temperature-adjusted estimate of your true pre-fermentation gravity.
- Corrected FG: Temperature-adjusted estimate of your true post-fermentation gravity.
- ABV (%): Approximate alcohol strength, based on OG and FG drop.
- Apparent Attenuation (%): The percentage of fermentable sugars consumed by yeast.
- Plato (°P): Another gravity scale often used in professional and international brewing.
Typical gravity ranges by style
Use these as rough reference points, not strict rules:
- American Light Lager: OG 1.028–1.040, FG 1.002–1.008
- Pale Ale: OG 1.045–1.060, FG 1.008–1.014
- IPA: OG 1.055–1.075, FG 1.010–1.018
- Porter/Stout: OG 1.048–1.075, FG 1.010–1.020
- Double IPA/Strong Ale: OG 1.070–1.100+, FG 1.012–1.024
Common gravity mistakes (and how to avoid them)
Reading too early
Early FG samples can make your beer seem under-attenuated. Always take stable readings over 2–3 days before packaging.
Ignoring temperature correction
A warm sample can throw your data off by several gravity points. That can be enough to misjudge mash efficiency, ABV, or fermentation health.
Using uncalibrated equipment
Check your hydrometer in distilled water at the calibration temperature. It should read 1.000. If not, apply your instrument offset each time.
Practical tips for better brew-day gravity control
- Mix wort thoroughly before taking pre-boil and post-boil samples.
- Degas fermented beer samples before FG reading to avoid buoyancy errors.
- Track OG, FG, mash temp, yeast strain, and fermentation temp in a brew log.
- Compare attenuation against yeast manufacturer ranges to diagnose issues.
- Use consistent sampling technique to make batch-to-batch trends meaningful.
Bottom line
Gravity data is one of the most powerful feedback loops in homebrewing. A good brew gravity calculator turns raw readings into actionable brewing insight: accurate OG/FG, realistic ABV, and clear fermentation performance. Use the numbers, adjust your process, and each batch gets better.