Og Fg Calculator

In brewing—whether beer, cider, mead, or other fermented beverages—precision is everything. Two of the most critical measurements for determining alcohol content, fermentation progress, and recipe balance are Original Gravity (OG) and Final Gravity (FG). The OG FG Calculator is a specialized brewing tool designed to quickly and accurately calculate these values, ensuring your homebrew or commercial batch turns out just right.

OG/FG ABV Calculator (Homebrew Alcohol Content)

This calculator estimates Alcohol By Volume (ABV) from OG and FG using the common formula:
ABV ≈ (OG – FG) × 131.25
Example: OG = 1.055, FG = 1.012 → ABV ≈ (1.055 – 1.012) × 131.25 = 5.63%

How to Use the OG FG Calculator

Using an OG FG Calculator is straightforward, but a basic understanding of brewing measurements helps ensure accuracy.

Step-by-Step Guide:

  1. Measure Original Gravity (OG):
    • Take a sample of your wort before fermentation starts.
    • Use a hydrometer or refractometer to determine its specific gravity reading (e.g., 1.050).
  2. Measure Final Gravity (FG):
    • After fermentation ends, take another sample and measure again (e.g., 1.010).
  3. Enter Values into the Calculator:
    • Input your OG and FG readings in the designated fields.
  4. View Results:
    • The calculator will instantly determine ABV and other related values such as attenuation percentage.
  5. Analyze and Adjust:
    • Use the results to evaluate recipe performance and make adjustments for future brews.

OG FG Calculator Formula

The ABV from OG and FG is calculated using a brewing-specific formula. A common one is:

ABV (%) = (OG – FG) × 131.25

Where:

  • OG = Original Gravity reading
  • FG = Final Gravity reading
  • 131.25 = constant based on alcohol density and water weight

Example Calculation

Let’s assume you brewed an ale with:

  • Original Gravity (OG): 1.060
  • Final Gravity (FG): 1.015

Step 1 – Subtract FG from OG:
1.060 – 1.015 = 0.045

Step 2 – Multiply by constant:
0.045 × 131.25 = 5.91

Result: Your beer has an ABV of 5.91%.

Why OG & FG Matter in Brewing

  1. Alcohol Content Estimation:
    • Without OG and FG, it’s impossible to calculate ABV accurately.
  2. Fermentation Progress Tracking:
    • Comparing gravity readings helps you know when fermentation is complete.
  3. Recipe Reproducibility:
    • By documenting OG and FG, you can consistently reproduce the same beer style.
  4. Flavor and Body Assessment:
    • Higher FG usually means more residual sweetness, while lower FG indicates a drier beer.

Helpful Tips for Accurate Readings

  • Temperature Correction: Hydrometer readings vary with liquid temperature—use a correction chart.
  • Avoid Foam in Samples: Foam can skew readings; degas samples before measurement.
  • Calibrate Equipment: Regularly check hydrometers and refractometers for accuracy.
  • Take Multiple Readings: Especially before bottling, to ensure fermentation has truly ended.

Practical Example for Homebrewers

You’re brewing a stout and want it to have a smooth mouthfeel and around 6% ABV.

  • Your OG reading: 1.065
  • Your FG reading: 1.020

ABV = (1.065 – 1.020) × 131.25
ABV = 0.045 × 131.25 = 5.91%

Since the FG is on the higher side, the beer will have more body and sweetness compared to a drier brew with an FG around 1.010.

Advantages of Using an Online OG FG Calculator

  • Saves Time: No manual math required.
  • Reduces Errors: Automated formulas ensure accuracy.
  • Accessible Anywhere: Works on desktop, tablet, or mobile.
  • Ideal for Beginners & Pros: Simplifies brewing science for everyone.

Common Brewing Targets

  • Light Beer: OG 1.030–1.040, FG 1.005–1.010, ABV 3–4%
  • Pale Ale: OG 1.045–1.055, FG 1.010–1.015, ABV 4.5–5.5%
  • IPA: OG 1.060–1.075, FG 1.010–1.018, ABV 6–7.5%
  • Stout: OG 1.050–1.070, FG 1.015–1.025, ABV 5–7%

20 Frequently Asked Questions (FAQs)

1. What is Original Gravity in brewing?
It’s the specific gravity of wort before fermentation, indicating sugar concentration.

2. What is Final Gravity?
It’s the specific gravity after fermentation, showing how much sugar remains.

3. How does OG affect ABV?
Higher OG generally leads to higher alcohol potential.

4. Can Final Gravity be higher than Original Gravity?
In normal fermentation, no—unless measurement errors occur.

5. What tools measure OG and FG?
Hydrometers and refractometers are most common.

6. How accurate is an online OG FG calculator?
Very accurate if your gravity readings are correct.

7. Can I use a refractometer for FG?
Yes, but you must apply alcohol correction formulas.

8. What is attenuation?
The percentage of sugars fermented, calculated from OG and FG.

9. Does temperature affect readings?
Yes, readings must be adjusted based on sample temperature.

10. Is OG affected by mash temperature?
Yes, higher mash temps produce more unfermentable sugars, increasing FG.

11. Can I skip OG measurement?
Not if you want to calculate ABV accurately.

12. What if fermentation stops early?
You may get a higher FG than expected—could indicate stuck fermentation.

13. Does yeast strain affect FG?
Yes, some yeasts ferment more completely than others.

14. Is it possible to have negative attenuation?
No, unless readings are wrong.

15. What is the ideal FG for an IPA?
Typically between 1.010–1.016 depending on dryness desired.

16. Can I increase ABV after fermentation?
Yes, by adding fermentable sugars and re-fermenting.

17. Does higher FG mean sweeter beer?
Usually yes, due to residual sugars.

18. Can OG be too high?
Yes, it can stress yeast and lead to incomplete fermentation.

19. How often should I take FG readings?
At least two identical readings over 24–48 hours before bottling.

20. What if my FG is much lower than expected?
The beer may be drier and more alcoholic than planned—adjust recipe next time.