A brewer measures original gravity (OG) before fermentation and final gravity (FG) after. The drop converts to alcohol by volume with a standard factor — the classic ABV formula.
The example
OG 1.050, FG 1.010.
| A | B | |
|---|---|---|
| 1 | Item | Value |
| 2 | (1.050−1.010)×131.25 | — |
| 3 | ABV | → ~5.25% |
The formula
The formula:
How it works
How it works:
- OG (before fermentation) and FG (after) are specific-gravity readings.
- The drop (OG − FG) reflects sugar converted to alcohol.
- Multiply by 131.25 for ABV percent (a common approximation).
- Use a more precise formula at high ABV; 131.25 is standard for typical beers.
The 131.25 factor is an approximation that’s great for normal-strength beer. It assumes a roughly linear relationship between gravity drop and alcohol, which holds well up to ~6–7% ABV and drifts a bit at imperial strengths, where brewers use a more complex formula. For a food-truck or taproom menu, OG−FG times 131.25 is plenty accurate. Always take temperature-corrected gravity readings.
Try it: interactive demo
Original gravity and final gravity.
Variations
Apparent attenuation
Sugar fermented:
Calories (approx)
Per 12 oz:
More precise ABV
High gravity:
Pitfalls & errors
Temperature-correct. Adjust gravity readings to the hydrometer’s calibration temp.
131.25 is standard. Use the precise formula for very high ABV.
Gravity format. Use 1.050 form (not 50 points) with this factor.
Practice workbook
Frequently asked questions
How do I calculate ABV from gravity in Excel?
What's apparent attenuation?
Is 131.25 always accurate?
Stop fighting formulas. Learn them in a day.
This recipe is one of hundreds of real-world formulas we teach. Our Excel Formulas & Functions class covers lookups, logic, text, and dynamic arrays hands-on — live in Dallas–Fort Worth, Houston, Austin, Oklahoma City, Denver, or online.
See the Formulas & Functions Class