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ABV計算ツール（OG→FG＋屈折計）

初期比重と最終比重から、シンプル式・アドバンス式・ダニエルズ式でビールのABVを計算。屈折計補正（WCF）と減衰率、SG↔Brix↔Plato切り替えにも対応。

初期比重(OG) 発酵前の比重測定値。

最終比重(FG) 発酵後の比重測定値。

入力単位

計算式

ウォート補正係数屈折計のFG補正に使用します(デフォルト1.04)。

屈折計FG補正

アルコール度数(ABV)

6.30 %

アテニュエーション 80.0% ・12ozあたりのカロリー 200

指標	値

計算の仕組み

簡易式: ABV% = (OG − FG) × 131.25.

高精度式(Daniels法): ABV% = (76.08 × (OG − FG) / (1.775 − OG)) × (FG / 0.794).

Brix → SG: SG = 1 + (Brix / (258.6 − (Brix/258.2)×227.1)).

屈折計FG補正(Sean Terrill法): FG = 1.0000 − 0.0044993×OGb + 0.011774×FGb + 0.00027581×OGb² − 0.0012717×FGb² − 0.00000728×OGb³ + 0.000063293×FGb³ — まずBrix測定値にウォート補正係数(デフォルト1.04)を適用してください。

アテニュエーション(発酵度): (OG − FG) / (OG − 1). 12ozあたりのカロリー: 1.5 × ABV + 0.4 × (residual gravity points) × 3.

計算の仕組み

Two formulas are available. Simple is the standard homebrew shortcut, ABV% = (OG − FG) × 131.25, which turns 1.060 down to 1.012 into 6.30%. Advanced (Daniels) uses 76.08 × (OG − FG) / (1.775 − OG), multiplied by FG / 0.794, and reads 6.51% on the same numbers. Apparent attenuation is calculated separately as (OG − FG) / (OG − 1), giving 80.0% for that pair. Brix and Plato entries are converted to specific gravity first with the usual cubic polynomial.

The input unit and the formula choice matter most. The two equations agree closely on ordinary beers but diverge as gravity climbs — about 0.2 points apart at 1.060, but roughly 0.8 apart on a 1.090 tripel, where Daniels is the better bet. If you took your final reading with a refractometer, set the input unit to Brix and turn on the Sean Terrill correction, which divides both readings by the wort correction factor (default 1.04) before running a cubic that compensates for alcohol.

The refractometer correction only fires when the input unit is set to Brix — leave it on SG and the toggle silently does nothing. Plato is converted with exactly the same polynomial as Brix, which is close but not identical, since the two scales differ slightly at higher gravities. And every result assumes a normal beer fermentation: unfermentable additions, priming sugar, spirit fortification and heavy kettle caramelisation all move the true alcohol away from what gravity difference alone predicts.

よくある質問

What is the formula for ABV from OG and FG?

The simple version is (OG − FG) × 131.25. An original gravity of 1.060 finishing at 1.012 gives a difference of 0.048, which multiplied by 131.25 comes to 6.30% ABV. The tool also converts that to approximate alcohol by weight at 79% of the ABV figure.

Why is my refractometer final gravity reading wrong?

Alcohol bends light differently from sugar, so a refractometer over-reads once fermentation has started. Set the input unit to Brix and switch Refractometer FG correction to On (Sean Terrill) — the correction is skipped entirely if the unit is left on SG.

What wort correction factor should I use?

The default is 1.04, which suits most refractometers on beer wort. The field accepts 0.5 to 1.5. To find yours, measure the same cooled sample with both a refractometer and a hydrometer and divide the Brix reading by the hydrometer-derived Brix.

What is apparent attenuation and what does 80% mean?

It is the fraction of the original gravity points the yeast consumed, calculated as (OG − FG) divided by (OG − 1). Going from 1.060 to 1.012 uses 48 of 60 points, which is 80% — a typical, healthy finish for a clean ale yeast.

When should I use the Advanced (Daniels) formula?

On strong beers. The two formulas track each other closely below about 1.070 but pull apart above it, because the simple multiplier assumes a linear relationship that breaks down at high gravity. On a 1.090 tripel the gap is close to 0.8 percentage points.

別名

abv calculatorog fg to abvrefractometer calculatorhomebrew abv

ABV計算ツール（OG→FG＋屈折計）

計算の仕組み

よくある質問

別名

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