Brewing · Specific Gravity
Enter original and final gravity to get ABV, apparent and real attenuation, gravity points, °Plato, and calories — live as you type.
Worked example
1.055 → 1.012
A 38-point drop — change readings live in the calculator below.
Live calculator · updates as you type
Gravity points are the last three digits of specific gravity (1.055 = 55 points). Apparent attenuation uses raw gravity; real attenuation corrects for alcohol using degrees Plato, so it always reads lower.
From your OG and FG
Typical OG / FG / attenuation by style
Gravity guide
Every number that matters — alcohol, attenuation, calories — comes from the gap between your original and final gravity. This guide shows how to read it and what it means.
1.050 in gravity points — the brewer's shorthand.
A typical apparent attenuation range.
Real attenuation is roughly four-fifths of apparent.
The gravity drop drives both alcohol and attenuation. Real attenuation and real extract add a Plato correction for the alcohol present.
Enter your original gravity and final gravity as specific gravity values — for example 1.055 and 1.012. The calculator immediately returns ABV, apparent and real attenuation, the gravity drop, real extract, and an approximate calorie count per serving.
Use it to confirm a batch has finished, to compare a reading against your target, or to record the numbers in a brew log. Everything recalculates live as you adjust either reading.
Specific gravity measures density relative to water at 1.000. Dissolved sugar makes wort, must, or juice denser, so a higher original gravity means more fermentable sugar and a higher potential alcohol content.
As yeast convert sugar to alcohol and CO₂, density falls. The gap between original and final gravity is the engine behind every other number on this page — alcohol, attenuation, and calories all derive from that drop.
Gravity points are the last three digits of specific gravity: 1.050 is 50 points. Brewers talk in points because it makes gravity drops easy — 50 down to 12 is a clean 38-point drop. The calculator shows points beside each reading.
Degrees Plato express the same sugar content as a percentage by weight and are common in professional brewing. Plato is what makes real attenuation and real extract possible, since those corrections are defined on the Plato scale.
Apparent attenuation comes straight from gravity and reads high because alcohol is lighter than water and drags the final gravity down. It is the number most brewers quote day to day.
Real attenuation corrects for that alcohol using Plato and always reads lower — roughly four-fifths of the apparent figure. It reflects the true fraction of sugar fermented, which matters for calorie and body calculations.
ABV is estimated as (OG − FG) × 131.25 — a bigger gravity drop means more alcohol. The calculator reports this instantly so you can confirm a batch hit its target strength before packaging.
Calories combine alcohol and leftover sugar into a per-serving figure. Drier beers with low final gravity have fewer calories than sweeter, higher-finishing ones at the same ABV, because residual sugar adds calories of its own.
If attenuation reads above 100% or ABV looks impossible, check for a transposed reading or a decimal slip. Confirm the hydrometer reads 1.000 in plain water at its calibration temperature and correct for sample temperature when hot.
If gravity has stalled higher than expected, give the yeast warmth and time, rouse gently, and re-read after a couple of days before deciding the fermentation is truly stuck.
Common questions about OG, FG, gravity points, and attenuation.
Specific gravity is the density of your wort or must relative to water (1.000). Dissolved sugar raises it, so a reading of 1.050 means the liquid is 5% denser than water. Original gravity (OG) is measured before fermentation and final gravity (FG) after, and the drop between them tells you how much sugar became alcohol.
Gravity points are the last three digits of specific gravity — 1.050 is 50 points, 1.012 is 12 points. Brewers use points as shorthand and to talk about gravity drops (50 down to 12 is a 38-point drop). This calculator shows points alongside specific gravity and °Plato.
Apparent attenuation is calculated straight from gravity and reads high because alcohol is less dense than water, which pulls the final gravity down. Real attenuation corrects for that alcohol using degrees Plato and always reads lower — typically around 80% of the apparent figure. Apparent is the everyday number; real attenuation is the true fraction of sugar fermented.
The standard estimate is (OG − FG) × 131.25. A drop from 1.055 to 1.012 is 0.043, so about 5.6% ABV. This calculator applies that formula and also reports attenuation and calories. For very high-gravity brews a more complex formula reads slightly higher.
A stable gravity across two or three days usually means fermentation is complete. If it stalls higher than expected, the cause is often yeast reaching its alcohol tolerance, low temperature, under-pitching, or unfermentable sugars. Confirm the reading is stable before packaging or calling it stuck.
Calories come from both alcohol and residual sugar. The estimate combines ABV and final gravity into calories per 12 oz (355 ml) serving. It is an approximation — real values shift with residual sugar, serving size, and any adjuncts.