BrewCalc

Brewing ABV Calculator

From gravity readings to alcohol percentage.

Original Gravity (OG)

Final Gravity (FG)

ABV

5.25%

Apparent Attenuation: 80%

What you entered

Original Gravity (OG): 1.05Final Gravity (FG): 1.01

1
Gravity drop
1.05 - 1.01= 0.04
2
ABV = gravity drop x 131.25
0.04 x 131.25= 5.25%
3
Apparent attenuation
((1.05 - 1.01) / (1.05 - 1)) x 100= 80%

Result

ABV: 5.25%

Alcohol by volume from original and final gravity

ABV is roughly the gravity drop multiplied by 131.25. Apparent attenuation is the share of sugar the yeast consumed.

Style	Original gravity	Final gravity	ABV	Apparent attenuation
Session ale	1.045	1.008	4.86%	82.2%
Pale ale	1.050	1.010	5.25%	80.0%
IPA	1.055	1.012	5.64%	78.2%
Amber ale	1.060	1.015	5.91%	75.0%
Strong ale	1.080	1.020	7.88%	75.0%
Imperial stout	1.090	1.018	9.45%	80.0%

Most ale yeasts attenuate 72% to 82%. A final gravity far above the expected range suggests a stalled fermentation; far below suggests a wild yeast or bacterial infection. The 131.25 multiplier drifts slightly high above about 8% ABV.

The simple ABV formula

ABV ≈ (OG − FG) × 131.25 — this approximation works because the drop in specific gravity directly reflects how much sugar the yeast converted to alcohol and CO₂, and 131.25 is the empirically derived conversion factor.

What apparent attenuation tells you

Apparent attenuation measures what percentage of the original sugars were consumed — most ales finish at 70–80% apparent attenuation, while a very dry beer might hit 85%+ and a sweet stout might be under 65%.

Frequently asked questions

My OG was 1.055 and FG is 1.012 — what's the ABV?

ABV = (1.055 − 1.012) × 131.25 = 5.6%. That's typical for an American pale ale or IPA — right in the middle of the range for a standard-strength craft beer.

How is the ABV calculator different from the yeast pitch rate calculator?

The ABV calculator works after fermentation — it measures the alcohol produced from the gravity drop. The yeast pitch rate calculator works before fermentation — it tells you how many yeast cells to pitch based on wort volume and OG to ensure healthy fermentation.

Why does the 131.25 formula sometimes disagree with refractometer readings?

Alcohol changes a refractometer's refractive index reading, making FG appear higher than it actually is. You need a correction formula for post-fermentation refractometer readings, or use a hydrometer for FG instead.

My beer finished at 1.000 — is that possible?

Yes, though unusual. Very dry styles with highly fermentable sugars (like brut IPA using amylase enzyme) can finish at or even below 1.000. An FG of 1.000 with OG of 1.050 gives 6.6% ABV and ~100% apparent attenuation.

Does the formula work for wines and meads?

The standard formula works up to about 10% ABV. Above that, a more accurate alternate formula — ABV = (76.08 × (OG − FG) / (1.775 − OG)) × (FG / 0.794) — is recommended because the simple formula increasingly underestimates at higher alcohol levels.