What is apparent attenuation?

Apparent attenuation is the percentage of original gravity points that have been fermented. It is called "apparent" because alcohol is less dense than water, making the gravity reading appear lower than the true extract remaining. Formula: AA% = (OG - FG) / (OG - 1.000) × 100.

What is real attenuation?

Real attenuation corrects for the lower density of alcohol and gives the true percentage of extract consumed. It is approximately 81.5% of apparent attenuation (RA ≈ AA × 0.815). This is more useful for comparing yeast efficiency.

How do I know if fermentation is complete?

Take gravity readings 48 hours apart. If the FG has not changed, fermentation is likely complete. For most ales, expect FG between 1.008 and 1.016. Compare your apparent attenuation to your yeast strain's documented range (usually 70–80% for ale yeasts).

What gravity scale should I use?

This calculator uses specific gravity (SG) points, which are decimal values like 1.050 for OG and 1.012 for FG. Both Plato and Brix scales can be converted: SG ≈ 1 + (Plato / 258.6). Most hydrometers are calibrated in SG.

What causes stuck fermentation?

Common causes include fermenting below the yeast's minimum temperature, nutrient deficiency, unhealthy pitching rate, or too-high osmotic stress from very high OG worts. Apparent attenuation below 65% on a standard ale recipe usually signals a problem.

Can I use refractometer readings for FG?

Raw refractometer readings are inaccurate after fermentation because alcohol skews the reading. You must apply a correction formula (Brix to SG with alcohol correction) before entering the value. This calculator accepts corrected SG values only.

Final Gravity Calculator

Enter your original gravity and current gravity to calculate apparent attenuation, remaining extract, and whether fermentation is complete.

Gravity Readings

Original Gravity (OG)

Measured before pitching yeast (typical range: 1.030–1.100)

Final / Current Gravity (FG)

Measured after fermentation slows (typical range: 1.005–1.020)

Yeast Attenuation Range (optional)

Min %

Max %

From your yeast strain data sheet — used for fermentation status check

Enter gravity readings and click Calculate

Summary

The Final Gravity Calculator helps homebrewers determine how much fermentable sugar yeast has consumed during fermentation. By comparing your original gravity (OG) before pitching yeast with your current or final gravity (FG), the tool calculates apparent attenuation — a key indicator of fermentation health and beer dryness. It also estimates real attenuation, which accounts for the masking effect of alcohol on refractometer and hydrometer readings.

How it works

Measure and enter your original gravity (OG) taken before pitching yeast.
Measure and enter your current or final gravity (FG) using a hydrometer or refractometer.
The calculator computes apparent attenuation as a percentage of fermentable sugars consumed.
Real attenuation is derived by applying a correction factor for alcohol masking.
Compare your attenuation against your yeast strain's expected range to judge fermentation completeness.

Use cases

Verify that fermentation has reached its expected final gravity before packaging.
Diagnose stuck fermentation by comparing actual vs. expected attenuation.
Calculate the dryness or residual sweetness of your finished beer.
Track fermentation progress across multiple gravity readings.
Compare yeast strains by their real-world attenuation performance.
Estimate remaining fermentable extract to decide whether to add adjuncts.

Frequently Asked Questions

Last updated: 2026-05-29 · Reviewed by Nham Vu