Final Gravity Calculator

If you’re a homebrewer, you already know that brewing beer is as much a science as it is an art. From selecting the right grains to achieving the perfect fermentation, precision plays a key role in ensuring your beer tastes exactly how you intended. One critical measurement in this process is Final Gravity (FG) — the reading you take at the end of fermentation to understand the beer’s density and sugar content.

Final Gravity (FG) Calculator

Our Final Gravity Calculator is designed to make this step quick and accurate. Whether you’re brewing a light lager or a rich stout, knowing your FG helps you determine alcohol content, sweetness, and overall drinkability. This guide will explain what final gravity is, how to use the calculator, the formula behind it, and why it matters so much in brewing.

What is Final Gravity?

Final Gravity (FG) is the measurement of the specific gravity of beer or wort after fermentation is complete. It reflects how much residual sugar remains, indicating how dry or sweet the beer will be. FG is measured using a hydrometer or refractometer and is typically lower than the original gravity (OG) since yeast converts much of the sugar into alcohol and carbon dioxide during fermentation.

For example:

  • A high FG means more unfermented sugar, resulting in a sweeter beer.
  • A low FG means most sugars have been consumed, resulting in a drier beer.

Why is Final Gravity Important?

Measuring FG is essential for several reasons:

  1. Determines Alcohol By Volume (ABV) – Using OG and FG, you can calculate the exact ABV of your beer.
  2. Indicates Fermentation Completion – Helps ensure fermentation has fully finished before bottling, reducing the risk of over-carbonation.
  3. Affects Flavor & Mouthfeel – Higher FG creates a fuller body and sweetness, while lower FG gives a crisp, dry finish.
  4. Quality Control – Repeated batches can be monitored for consistency using FG measurements.

Formula for Final Gravity Calculation

While FG is typically measured directly, it can also be calculated based on Original Gravity and attenuation percentage.

The general formula is:

FG = OG – ((OG – 1) × (attenuation percentage ÷ 100))

Where:

  • OG = Original Gravity (before fermentation)
  • Attenuation percentage = Yeast’s efficiency in converting sugar to alcohol
  • FG = Final Gravity

If you also want to calculate ABV from FG and OG, the formula is:

ABV (%) = (OG – FG) × 131.25

How to Use the Final Gravity Calculator

Using our Final Gravity Calculator is simple:

  1. Measure Original Gravity (OG) – Before fermentation, use a hydrometer to get your OG reading.
  2. Enter Attenuation Percentage or Final Hydrometer Reading – Based on your yeast strain’s characteristics or actual hydrometer reading after fermentation.
  3. Click Calculate – The tool will instantly show your FG and optionally the ABV.
  4. Record Your Results – Keep track for recipe adjustments and future brews.

Example Calculation

Let’s say:

  • OG = 1.060
  • Attenuation = 75%

Step-by-step:

  1. OG – 1 = 1.060 – 1 = 0.060
  2. Multiply by attenuation: 0.060 × 0.75 = 0.045
  3. Subtract from OG: 1.060 – 0.045 = 1.015

Your Final Gravity would be 1.015.
If you want ABV:
(1.060 – 1.015) × 131.25 = 5.91% ABV

Helpful Brewing Tips for Accurate FG

  • Always take multiple readings over 2–3 days to confirm fermentation is complete.
  • Temperature correction is important — hydrometer readings vary based on liquid temperature.
  • Avoid contamination when taking samples; it can alter fermentation and flavor.
  • Know your yeast strain — different strains have different attenuation ranges.

Common FG Ranges for Beer Styles

  • Light Lagers: 1.006 – 1.010
  • IPAs: 1.010 – 1.016
  • Porters/Stouts: 1.012 – 1.020
  • Belgian Ales: 1.008 – 1.014
  • Wheat Beers: 1.008 – 1.012

These are averages; your recipe and yeast choice will affect FG.

Benefits of Using a Final Gravity Calculator

  1. Saves time compared to manual calculations.
  2. Reduces the risk of errors in ABV estimation.
  3. Helps you hit target beer profiles consistently.
  4. Great for both beginner and professional brewers.

20 Frequently Asked Questions (FAQs)

Q1: What is considered a good final gravity?
A1: It depends on beer style, but most fall between 1.006 and 1.020.

Q2: How do I know if fermentation is complete?
A2: Take two FG readings over 48 hours. If they’re the same, fermentation is likely complete.

Q3: Can FG be higher than OG?
A3: In normal fermentation, no. If it is, a measurement error likely occurred.

Q4: Does yeast type affect FG?
A4: Yes, yeast attenuation rate directly influences FG.

Q5: How can I lower my FG?
A5: Use highly attenuative yeast and ensure proper fermentation temperature.

Q6: Can I use a refractometer for FG?
A6: Yes, but you need a correction formula due to alcohol’s effect on readings.

Q7: What happens if my FG is too high?
A7: The beer may be sweeter than intended; possible causes include stalled fermentation.

Q8: Can final gravity change after bottling?
A8: If bottling before fermentation is complete, FG can drop, causing over-carbonation.

Q9: Does mash temperature affect FG?
A9: Yes, higher mash temps produce more unfermentable sugars, leading to higher FG.

Q10: What’s the difference between FG and OG?
A10: OG is before fermentation; FG is after fermentation.

Q11: Is FG the same for wine and beer?
A11: The concept is similar, but wine usually has a much lower FG.

Q12: How do I fix a stuck fermentation?
A12: Try gently swirling the fermenter, warming slightly, or adding more yeast.

Q13: Can FG readings vary with altitude?
A13: Not significantly; temperature has a bigger impact than altitude.

Q14: What’s the impact of adjunct sugars on FG?
A14: They can lower FG since simple sugars ferment completely.

Q15: Does aging beer affect FG?
A15: FG remains stable if fermentation is complete; flavor changes over time.

Q16: How long after fermentation should I take FG?
A16: Wait at least 1–2 days after visible fermentation stops.

Q17: Can I predict FG before brewing?
A17: Yes, based on OG and yeast attenuation percentage.

Q18: Is FG important for non-alcoholic beer?
A18: Yes, it helps control sweetness and mouthfeel.

Q19: Can improper sanitation affect FG?
A19: Yes, contamination can stall or alter fermentation.

Q20: How often should I calibrate my hydrometer?
A20: At least once a year or after any noticeable reading inconsistencies.

This Final Gravity Calculator is an indispensable brewing tool, helping you achieve the desired sweetness, dryness, and ABV for your beer. Whether you’re a hobbyist or a pro brewer, accurate FG measurement ensures every batch meets your expectations.