What is the difference between apparent and real attenuation?

Apparent attenuation is calculated directly from the gravity change and overstates actual sugar conversion because alcohol is less dense than water, making the FG read lower than it truly is. Real attenuation corrects for this by multiplying apparent attenuation by approximately 0.814, giving a more accurate measure of how much fermentable extract was actually consumed.

What attenuation should I expect from my yeast?

Lager yeasts typically achieve 73–77% apparent attenuation. Most ale yeasts fall in the 73–79% range. High-attenuation strains (such as Chico or certain Belgian yeasts) can exceed 80%. Your actual result depends on mash temperature, adjunct percentage, and pitching conditions.

How do I convert degrees Plato to specific gravity?

A commonly used approximation is SG ≈ 1 + (°P / 250). For example, 12 °P ≈ 1.048 SG. This tool applies that conversion automatically when you select the Plato input mode.

Why is residual extract shown in degrees Plato?

Residual extract — the unfermented sugars left in the finished beer — is conventionally expressed in degrees Plato because it maps directly to the Balling scale used in brewing calculations. It tells you how sweet or full-bodied the beer will taste.

My calculated attenuation is outside the yeast spec — what does that mean?

Lower than expected attenuation often indicates a stuck fermentation, under-pitching, high mash temperature, or insufficient yeast nutrients. Higher than expected attenuation can result from highly fermentable wort, diastaticus contamination, or a mash that was too cold.

Alcohol Attenuation Calculator

Enter original and final gravity to calculate apparent attenuation, real attenuation, ABV, and residual extract for your homebrew.

Gravity Readings

Input Unit

Original Gravity (OG)

Before fermentation, e.g. 1.052

Final Gravity (FG)

After fermentation is complete, e.g. 1.010

Quick Presets

Results

Enter gravity readings and click Calculate.

Typical Yeast Attenuation Ranges

Lager yeast 73–77% apparent

Ale yeast 73–79% apparent

High-attenuation strains 80%+ apparent

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Summary

This tool calculates yeast attenuation from your original gravity (OG) and final gravity (FG) readings. Apparent attenuation tells you what percentage of fermentable sugars were consumed based on gravity change alone. Real attenuation corrects for the different density of alcohol versus water, giving a more accurate picture of actual sugar conversion. You can enter gravity in specific gravity (SG) format or degrees Plato — the calculator converts automatically.

How it works

Measure original gravity (OG) before fermentation using a hydrometer or refractometer.
After fermentation is complete, measure final gravity (FG) the same way.
Select your input unit: Specific Gravity (e.g. 1.050) or degrees Plato (e.g. 12.4).
Enter OG and FG in the chosen unit — the calculator converts to SG internally.
Apparent Attenuation is computed as ((OG - FG) / (OG - 1.000)) × 100.
Real Attenuation applies the Balling correction factor: Apparent Attenuation × 0.814.
ABV is estimated using the Miller simplified formula: (OG - FG) × 131.25.
Residual extract (°P) shows the unfermented sugars remaining in the finished beer.

Use cases

Determine whether fermentation has reached its expected attenuation for a yeast strain.
Diagnose a stuck fermentation by comparing actual vs. expected attenuation.
Compare lager, ale, and high-attenuation yeast performance across batches.
Calculate real attenuation for precise recipe formulation and mash efficiency checks.
Estimate ABV alongside attenuation without switching to a separate calculator.
Track batch-to-batch consistency for the same recipe across multiple brews.

Frequently Asked Questions

Last updated: 2026-06-15 · Reviewed by Nham Vu