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Specific Gravity to ABV

1 Specific Gravity (SG) = 0ABV (approx.) (% ABV)

By KAMP Inc. / UnitOwl · Last reviewed:

Result
0 % ABV
1 SG = 0 % ABV
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How to Estimate ABV from Specific Gravity?

To estimate ABV (alcohol by volume) from specific gravity readings, use the formula: ABV ≈ (OG - FG) × 131.25, where OG is original gravity and FG is final gravity. For example, a beer with OG 1.050 and FG 1.010 would have an ABV of approximately (0.050 - 0.010) × 131.25 = 5.25%. This is the most common calculation in homebrewing and is used to determine the alcohol content of finished beer, wine, cider, and mead. The key idea is that gravity falls as yeast turns sugar into alcohol and carbon dioxide. The bigger the drop between OG and FG, the more fermentable extract was consumed and the higher the finished ABV. This is why the same original gravity can yield very different alcohol levels depending on yeast attenuation and recipe design: a dry saison finishing at 1.004 will be noticeably stronger than a sweet stout that starts at the same OG but stops at 1.018. Brewers use this estimate for recipe design, competition entries, and packaging checks, although legal label claims are typically confirmed with more formal lab methods.

How to Convert Specific Gravity to ABV (approx.)

  1. Measure the original gravity (OG) of your wort before fermentation.
  2. Measure the final gravity (FG) after fermentation is complete.
  3. Subtract: OG - FG (e.g., 1.050 - 1.010 = 0.040).
  4. Multiply the difference by 131.25 to get approximate ABV percentage.
  5. For more precision, use the alternate formula: ABV = (76.08 × (OG - FG) / (1.775 - OG)) × (FG / 0.794).

Real-World Examples

Session IPA — OG 1.045, FG 1.008
ABV = (1.045 - 1.008) × 131.25 = 4.86%. A light, drinkable IPA.
Belgian tripel — OG 1.080, FG 1.012
ABV = (1.080 - 1.012) × 131.25 = 8.93%. A strong abbey-style ale.
Dry cider — OG 1.055, FG 0.998
ABV = (1.055 - 0.998) × 131.25 = 7.48%. Cider can ferment below 1.000 because the sugars are almost fully consumed.
Stout — OG 1.060, FG 1.018
ABV = (1.060 - 1.018) × 131.25 = 5.51%. The higher FG gives this stout a fuller body.
West Coast IPA — OG 1.068, FG 1.014
ABV = (1.068 - 1.014) × 131.25 = 7.09%. This is a typical strength range for a firmly bitter, modern IPA.

Quick Reference

Specific Gravity (SG)ABV (approx.) (% ABV)
10
2131.25
3262.5
5525
101181.25
151837.5
202493.75
253,150
506431.25
759712.5
10012993.8
25032681.3
50065493.8
1,000131,119

History of Specific Gravity and ABV (approx.)

The formula ABV = (OG - FG) × 131.25 is a simplified version of equations developed by brewing scientists in the 19th century. The constant 131.25 is derived from the relationship between sugar consumed and alcohol produced during fermentation. More precise formulas, like those published by Balling, Cutaia, and the ASBC (American Society of Brewing Chemists), account for the production of CO₂ and other fermentation byproducts, but the simple formula is accurate within about 0.5% ABV for most beers.

Common Mistakes to Avoid

  • Using only the OG without the FG. ABV depends on how much sugar the yeast consumed, not how much was present initially. You need both readings.
  • Taking the FG reading before fermentation is truly complete. If the gravity is still dropping, your ABV calculation will be too low. Wait until gravity is stable for 2-3 consecutive days.
  • Forgetting that this formula gives an approximation. For high-gravity beers (above 8% ABV), the simple formula tends to slightly underestimate. Use the more complex ASBC formula for precision.
  • Using a raw refractometer final reading as FG. Once alcohol is present, refractometer values must be corrected before you plug them into an ABV formula.
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Frequently Asked Questions

Why is the constant 131.25?
The constant derives from the stoichiometry of alcoholic fermentation. When yeast converts sugar to ethanol and CO₂, approximately 48.4% of the sugar by weight becomes ethanol. Combined with the density relationships between sugar solutions and ethanol, this yields the factor of approximately 131.25 when working with specific gravity units.
Can I estimate ABV from just the OG?
You can get a rough estimate by assuming typical attenuation (75%). For a beer with OG 1.060: estimated FG ≈ 1 + (0.060 × 0.25) = 1.015. Then ABV ≈ (0.060 - 0.015) × 131.25 = 5.9%. This is a rough guide only — actual attenuation varies significantly by yeast strain and recipe.
What is a normal final gravity for beer?
Most beers finish between 1.006 and 1.018. Dry styles (Belgian tripel, saison) may finish as low as 1.002-1.006. Full-bodied styles (milk stout, Scotch ale) may finish at 1.015-1.025. The FG depends on yeast attenuation, mash temperature, and the types of sugar present.
Can final gravity drop below 1.000?
Yes. Cider, mead, wine, and very dry beers can finish below 1.000 because ethanol is less dense than water. That is normal when most sugars ferment out completely.
Why is the simple ABV formula less accurate for strong beers?
At higher gravities, ethanol production and density effects become more pronounced, so the shortcut underestimates slightly. For double IPAs, barleywines, and strong meads, the more complex ASBC-style formula gives better precision.
Quick Tip

The converter on this page estimates ABV from a single gravity reading by assuming FG = 1.000 (full attenuation). For real brewing, always take both an OG and FG reading. A more practical use of the single-SG conversion is estimating the maximum potential ABV of a wort — what you would get if every bit of sugar fermented completely.

Sources & References