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Homebrew Beer ABV Calculator
Brewed your first batch and wondering if it's beer or acci dental rocket fuel? Plug in your hydrometer readings and find out how much alcohol you actually made.
Gravity Readings
Results
🍺 Style: Calculate to see
Understanding Beer Alcohol Content
The formula is simple algebra from high school: ABV = (OG - FG) × 131.25. But like most brewing, the devil's in the details. Your hydrometer readings tell the story of fermentation—how much sugar the yeast ate and converted to alcohol and CO₂.
💡 Real Talk from Mike Thompson, Certified Cicerone
Hydrometers lie when they're hot. Most are calibrated for 60°F. If your wort sample is 90°F and you take a reading, it's wrong—hot liquid is less dense, so you get a falsely LOW reading. Always cool your sample to 60-70°F or use an online temperature correction calculator. I've seen brewers think fermentation was done when it hadn't even started.
Original Gravity (OG): The Starting Line
Original Gravity measures how much sugar (and other dissolved solids) are in your wort before yeast touch it. Higher OG = more food for yeast = more potential alcohol.
Typical OG ranges:
- 1.030-1.040: Light lagers, session ales (3-4% ABV potential)
- 1.045-1.055: Standard ales, pale ales (4.5-5.5% ABV)
- 1.055-1.065: Amber ales, porters (5.5-6.5% ABV)
- 1.070-1.085: IPAs, stouts, Belgian strongs (7-9% ABV)
- 1.085-1.120+: Imperial anything, barleywines (9-14% ABV)
Water is 1.000. Anything above that is dissolved sugars. Each 0.001 increment = ~1 "gravity point."
Final Gravity (FG): The Finish Line
Final Gravity tells you what's LEFT after fermentation. It's never 1.000 (pure water) because yeast can't eat everything. Stuff they leave behind:
- Unfermentable sugars: Created by mashing at high temps (158°F+)
- Proteins and dextrins: Give body/mouthfeel
- Dead yeast particles: (hopefully not much)
Good FG ranges by style:
- 1.008-1.012: Dry finish (IPAs, saisons, dry stouts)
- 1.012-1.016: Balanced (pale ales, ambers, porters)
- 1.016-1.024: Sweet/full-bodied (milk stouts, barleywines, Belgians)
⚠️ Common Mistakes to Avoid
- Not temperature-correcting hydrometer readings: Hydrometers are calibrated for 60°F. Measuring hot wort at 90°F gives a falsely low reading. Always cool your sample or use a correction calculator.
- Bottling too early: "It's been 2 weeks, it must be done." Wrong. If gravity is still dropping, you're bottling potential bombs. Verify stable gravity for 3 consecutive days before bottling.
- Confusing apparent vs true attenuation: 75% attenuation doesn't mean 75% of sugar is gone. Alcohol is lighter than water, skewing the reading. Don't panic if your numbers seem "off" compared to lab stats.
- Judging by airlock activity: Bubbles stopped? Doesn't mean fermentation stopped. The bucket lid might just be leaky. Trust your hydrometer, not the bubbles.
Attenuation: How Hard Your Yeast Worked
Apparent attenuation = (OG - FG) / OG × 100%. It tells you what percentage of available sugars got eaten.
Example: OG 1.060 → FG 1.015
Attenuation = (1.060 - 1.015) / 1.060 × 100 = 75.5%
Attenu ation interpretations:
- 65-70%: Low attenuation (sweet beer, possible stuck fermentation)
- 70-80%: Normal (most ale yeasts land here)
- 80-90%: High attenuation (saison yeasts, Champagne yeast, super dry finish)
Low attenuation when you expected high? Your fermentation got stuck.
Why Fermentation Gets Stuck
Top 5 reasons your FG is too high:
- Too cold: Yeast slow down under 62°F. Ideal ale fermentation: 65-72°F.
- Under-pitched: Not enough yeast cells. Use a pitch rate calculator or liquid yeast starters.
- Old yeast: Check expiration dates. Dead yeast don't ferment. Obvious, but it happens.
- Mash temp too high: Mashing at 160°F+ creates unfermentable sugars. Drop to 148-154°F for more fermentable wort.
- Low oxygen: Yeast need O₂ in the first 12 hours to reproduce. Shake/aerate your wort before pitching.
Fixes if it's already stuck:
- Warm it up to 68-72°F
- Gently swirl the fermenter (rouse the yeast)
- Pitch fresh yeast (same strain or champagne yeast if desperate)
- Wait 5-7 more days and retest
Calories in Your Homebrew
Approximate formula: Calories/12oz ≈ (OG - FG) × 1200 + (FG × 100)
Or roughly: higher ABV + higher FG = more calories. A 5% pale ale with FG 1.012 has about 150 cal/12oz. An 8% imperial stout with FG 1.020? Closer to 250-300 cal. Beer isn't health food.
💡 Mike's Favorite Brewing Hack: Taste Gravity Samples
Don't dump that hydrometer sample. Taste it. Week 1 tastes sweet (high FG, lots of sugar). Week 2 less sweet, more boozy. When it stops changing flavor day-to-day, fermentation's done. Your mouth is a surprisingly good FG detector—and way more fun than staring at a hydrometer.
Hydrometer vs Refractometer
Hydrometer (glass tube):
- Pros: Cheap ($10), no math corrections, works for FG
- Cons: Needs ~200ml sample (wasteful), fragile (you WILL break it)
Refractometer (droplet tool):
- Pros: Only needs 2-3 drops, instant reading, doesn't waste beer
- Cons: Expensive ($30-60), requires math correction for FG (alcohol skews the reading), calibration drift
For beginners: hydrometer. For advanced brewers who hate wasting beer: refractometer + online correction calculators.
Reviewed by Mike Thompson
Certified Cicerone & Homebrewer (15+ years)
Mike has brewed over 300 batches. His worst mistake? Bottling a 1.020 FG beer that was still fermenting. The explosion woke up his entire apartment building.
Frequently Asked Questions
What's a normal ABV for homebrew beer?
Most ales land between 4.5-6.5% ABV. IPAs usually hit 6-7%. Imperial stouts can reach 8-12%. Under 4%? You made a session beer (or something went wrong). Over 10%? Congrats, you made rocket fuel. Yeast struggles past 12% without special strains.
How do I measure original and final gravity?
Use a hydrometer. Take a sample BEFORE pitching yeast (Original Gravity). Take another sample when fermentation stops—usually after 2 weeks (Final Gravity). FG should be stable for 3 days in a row. If it's still dropping, fermentation isn't done. BE PATIENT.
What if my FG is too high?
High FG means stuck fermentation—yeast quit early. Common causes: 1) Too cold (yeast hibernating), 2) Not enough yeast pitched, 3) Dead yeast (check expiration), 4) Mash temp too high (created unfermentable sugars). Try warming to 68-72°F and gently swirling the fermenter. Still stuck? Pitch fresh yeast.
Can I bottle if FG is still dropping?
HELL NO. Bottle bombs are real. If FG is still falling, fermentation is active. Bottle that and the CO2 has nowhere to go. Result: glass grenades exploding in your closet at 3am. Wait until FG is stable for 3 consecutive days. Your floors will thank you.