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How strong did my cider turn out?

Alcohol by volume from a starting and finishing hydrometer reading, with both of the formulas in common use shown side by side — because they disagree above about 1.070 and most calculators only give you one of them.

ABV from gravity

The reading before fermentation started.

The reading now, once it is stable over several days.

Alcohol by volume

6.8% ABV

Alternate formula: 6.9% ABV

How this is worked out
  1. Standard formula: (1.050 − 0.998) × 131.25 = 6.83% ABV
  2. Alternate formula: (76.08 × (OG − FG) ÷ (1.775 − OG)) × (FG ÷ 0.794) = 6.86% ABV
  3. Gravity drop: 52 points
What this assumes (4)
  • Both formulas are approximations fitted to measurements; neither is derived from first principles.
  • Below about 1.070 the two formulas agree closely, which is why the simple one is the one normally quoted.
  • Hydrometers are calibrated at a stated temperature, usually 20 °C. A reading taken on warm juice is low and on cold juice is high.
  • This is the alcohol produced by fermentation. Adding sugar after fermentation, or blending, changes the finished strength.

Why there are two formulas

Both are empirical fits to measurements rather than derivations from first principles, and they were fitted over different ranges. The simple linear form — gravity drop multiplied by 131.25 — is the one almost everyone uses, and below about 1.070 it is accurate enough that the difference is smaller than the error in reading a hydrometer.

Above that it over-reads, because the relationship between sugar consumed and alcohol produced stops being linear. For ordinary cider this rarely matters: apple juice seldom starts above 1.070. For an apple wine, a chaptalised batch or an ice cider it matters a great deal, and the alternate figure is the one to use.

Neither formula knows anything about what you did after fermentation. Back-sweetening, blending and dilution all change the finished strength, and none of them shows up in a pair of gravity readings.

Temperature

Hydrometers are calibrated at a stated temperature, usually 20 °C. A reading taken on a warm ferment reads low and one on cold cider reads high, and at the margins that is worth a few tenths of a percent.

Related tools

Where this reading comes from

Guides that reach this calculator, and what the number decides once you have it.