Gravity Point and Fermentability Calculator
Created by: Emma Collins
Last updated:
Estimate gravity points and predict FG/ABV from attenuation assumptions.
Gravity Point and Fermentability Calculator
HomebrewingEstimate gravity points, predicted FG, and ABV from attenuation
Related Calculators
What is a Gravity Point and Fermentability Calculator?
This calculator translates original gravity into points and uses expected attenuation to estimate where your beer may finish. It helps brewers anticipate body, dryness, and alcohol level before fermentation is complete.
By modeling fermentability up front, you can make better recipe decisions around mash profile, yeast choice, and fermentation strategy.
Formula and Prediction Method
Predicted FG = OG − ((OG−1)×Attenuation)
Gravity points are computed as $(SG-1)\times1000$. Total batch points help compare fermentable load across recipe sizes.
With a realistic attenuation assumption, the calculator predicts final gravity and ABV so you can evaluate likely flavor balance before brew day.
Example Output
At OG 1.060 and 75% attenuation, predicted FG is around 1.015, often yielding moderate body and medium dryness. Increasing attenuation assumptions lowers predicted FG and can sharpen perceived finish.
These predictions are most useful when compared against your own historic fermentation results.
Applications
Use this calculator when designing new recipes, adjusting mash temperatures, or evaluating yeast substitutions. It is also useful for aligning target profile with style expectations.
During fermentation planning, these estimates help set realistic FG and ABV checkpoints for quality control.
Prediction Tips
Use attenuation ranges from your specific yeast lot and process conditions rather than generic package claims alone.
Compare predicted and actual FG each batch to improve future recipe forecasting accuracy.
Frequently Asked Questions
What are gravity points?
Gravity points are a practical way to express extract concentration, calculated as $(SG-1) imes1000$. They make recipe comparisons easier across different volumes and strengths. Total batch gravity points are especially useful when sizing grain bills, evaluating scaling changes, and understanding how much fermentable potential is being delivered to fermentation.
What does fermentability mean?
Fermentability describes how much wort extract is likely to be consumed by yeast, influencing final gravity, dryness, and mouthfeel. Higher fermentability usually leads to lower FG and a drier finish, while lower fermentability leaves more residual body. Mash profile, yeast strain, oxygenation, and fermentation conditions all affect real fermentability outcomes.
Is attenuation exact?
No. Attenuation is an estimate range, not a fixed outcome. Yeast health, wort composition, fermentation temperature, and process control can shift final results from nominal expectations. Use calculator predictions as planning guidance, then compare against measured FG after fermentation to calibrate assumptions for your specific process and yeast behavior.
How can I improve prediction reliability?
Track expected versus actual FG for each recipe and yeast combination, then refine attenuation assumptions over time. Consistent mash temperature control and healthy pitch rates also improve predictability. Building a small house dataset quickly makes future gravity and fermentability planning much more accurate than relying only on generic manufacturer ranges.
Sources and References
- Fix, George. "Principles of Brewing Science: A Study of Serious Brewing Issues." 2nd Edition. Brewers Publications, 1999. Scientific analysis of fermentability, attenuation mechanisms, and wort composition effects on final gravity outcomes.
- Palmer, John J. "How to Brew: Everything You Need to Know to Brew Great Beer Every Time." 4th Edition. Brewers Publications, 2017. Comprehensive coverage of gravity calculations, extract measurements, and practical attenuation prediction for homebrewing applications.