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Demijohn / Calculators

ABV calculator for wine, mead and cider

Type your original gravity and your latest reading. Demijohn uses the standard formula for grape, fruit and cider and the alternate formula for mead and sugar musts, and shows the others next to it.

What are you making?
Measured before the yeast went in.
Your latest reading.
Readings taken warmer or colder than the hydrometer’s calibration?
Hydrometer calibrated at

Leave empty if the sample was at the calibration temperature.

Added sugar or honey after the OG reading?
Before the addition.
What you added

Sugar or honey added later never shows in the OG, so the ABV from OG and FG alone comes out too low.

Result

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How it’s worked out

Two formulas, and which one when

The standard formula is ABV = (OG − FG) × 131.25. The alternate formula (Hall, 1995) is ABV = 76.08 × (OG − FG) / (1.775 − OG) × FG / 0.794. They agree at low gravity and drift apart above about 1.070.

We compared both with the sugar actually in the must. For grape, fruit and cider musts the standard formula is closer (mean error 0.24 % against OIV potential alcohol from 1.080 to 1.110), because juice carries 8 to 12 % solids that are not sugar. For mead and sugar musts the alternate formula is closer: at 1.100 to 0.996 it gives 14.7 % where the standard formula says 13.7 %. That gap is the usual “my mead is stronger than the calculator says”.

Sugar or honey added later

Every gram added after the OG reading raises the gravity the yeast really started from. Demijohn works out an effective OG by mass balance: the batch as must mass and dissolved solids from the NBS Brix curve, plus each addition’s solids (sugar 100 %, honey 82.8 %). The ABV is then worked out from that effective OG.

Temperature

A hydrometer is only right at its calibration temperature. Readings are corrected with NBS Table 110 for sugar solutions before the ABV is worked out. The temperature calculator explains the correction.

Refractometer readings

Once alcohol is present a refractometer reads high, so a refractometer FG put straight into an ABV formula is wrong. Use a hydrometer for the final reading, or the refractometer correction in the app (Terrill’s formula, with a warning outside the range it was fitted on).

How sure is the number?

Every ABV is an estimate. Yeasts turn 16.5 to 17.2 g/L of sugar into 1 % alcohol (AWRI), so read the result as ±2 % of itself. Above about 1.130 the three formulas spread by more than 1 % ABV and the calculator says so.

Sources

  1. Hall, M. L., “Brew by the Numbers”, Zymurgy, Summer 1995 (alternate ABV formula)
  2. Terrill, S., refractometer and FG calculator v3.0 (Balling ABV)
  3. OIV, alcoholic strength by volume (ethanol 789.24 kg/m³ at 20 °C)
  4. AWRI, sugar to alcohol conversion: 16.5 to 17.2 g/L per % vol
  5. Wikipedia, “Brix”: NBS cubic fit for SG and °Bx, Buhl (2023) fit for °P
  6. Bates et al., NBS Circular C440 (1942), Tables 109, 110 and 114

Doses are estimates. Add in steps, test again, follow the product label. For personal use only.

Checked against the sources: October 25, 2026

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