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ABV-from-gravity calculator

Estimate ABV from an original and final gravity reading — a homebrewing convention, not an official measurement.

The ABV from Gravity calculator estimates alcohol by volume from your original and final gravity readings. It offers two brewing conventions — pick the one that fits your gravity range — and is a quick way to see roughly where a ferment landed.

Unlike the compliance-grade Tools calculators, this one is an estimate only — there is no government-recognized formula for gravity-based ABV. It's a homebrewing and distilling convention, and it is never valid for a tax or label filing. For anything that has to be exact, an actual measurement (distillation or densitometry, per TTB methods) governs, never this estimate. The calculator carries this warning prominently, and on the hub it sits in its own Estimates (non-regulatory) section, marked Not an official measurement, so it's never mistaken for the compliance-grade tools.

It's free, needs no account, and computes in your browser.

Open the calculator

  • On the public site: in the top navigation choose Tools, then — in the Estimates (non-regulatory) section — on the ABV from Gravity card choose Open calculator.
  • Inside the app: in the navigation choose Tools, then on the ABV from Gravity card choose Open calculator.

The calculator header shows a Non-regulatory estimate badge, and a highlighted note repeats that this is not an official or regulatory measurement.

Choose a formula

Under Formula you can pick the convention used for the estimate:

  • Standard (linear) — the default. The common ABV ≈ (OG − FG) × 131.25 rule of thumb. Best up to roughly 7% ABV.
  • High-gravity (Hall) — an alternate convention that's more accurate above roughly 7% ABV, for stronger worts and washes.

The calculator starts on Standard. If a Standard estimate lands above roughly 7% ABV, it nudges you to try the High-gravity (Hall) formula, since the linear rule of thumb starts to drift there.

Estimate ABV

  1. Under Formula, leave Standard (linear) selected, or choose High-gravity (Hall) for a stronger ferment.
  2. In Original gravity (OG), enter your original (pre-fermentation) specific gravity — a number between 0.5 and 2 (readings usually sit near 1.0, e.g. 1.050).
  3. In Final gravity (FG), enter your final (post-fermentation) specific gravity, in the same range.
  4. Estimated ABV appears, shown as a percentage, labelled with the formula in use.

OG should be the higher of the two numbers. If you enter an FG higher than the OG, there's no fermentation to estimate and the calculator prompts you to check your readings (Final gravity is higher than original gravity…) instead of showing a negative number.

Worked example — Standard (linear)

An ale that started at 1.050 and finished at 1.010, on the default Standard (linear) formula:

  1. Original gravity (OG): 1.050
  2. Final gravity (FG): 1.010

The calculator shows Estimated ABV 5.25% — because (1.050 − 1.010) × 131.25 = 5.25.

Worked example — High-gravity (Hall)

A high-gravity wash that started at 1.090 and finished at 1.010, with High-gravity (Hall) selected:

  1. Original gravity (OG): 1.090
  2. Final gravity (FG): 1.010

The calculator shows Estimated ABV 11.302% — the Hall convention, 76.08 × (1.090 − 1.010) ÷ (1.775 − 1.090) × (1.010 ÷ 0.794) = 11.302. (The Standard formula would read 10.5% for the same gravities; above ~7% ABV the two conventions diverge, which is why the calculator nudges you toward Hall there.)

When to reach for it

Reach for ABV from Gravity to eyeball how a ferment or wash came out from your hydrometer or refractometer gravities — a fast gut-check while you work. Keep in mind it's a rule of thumb: the real strength depends on the ingredients and the ferment, and any number that has to be exact comes from an actual measurement, not this estimate.