Frequently Asked Questions
How is ABV calculated from gravity readings?
The standard formula is ABV = (Original Gravity − Final Gravity) × 131.25. For example, OG 1.052 and FG 1.011 gives (1.052 − 1.011) × 131.25 = 5.38% ABV. This simple formula is accurate for beers up to about 6% ABV; above that, the alternate formula (Ritchie) or the real-extract formula gives a better estimate because alcohol skews the relationship between gravity drop and ethanol produced.
Why does my refractometer read wrong after fermentation?
A refractometer measures how light bends through the liquid, and alcohol bends light differently than sugar. After fermentation starts, the raw Brix reading reads too high because alcohol is present. You must apply an alcohol correction (the Terrill cubic equation is the modern standard) using both your original Brix reading and your current Brix reading. Never trust the raw Brix number of a fermented sample as final gravity.
What is the Terrill refractometer correction formula?
Sean Terrill's cubic equation converts your two Brix readings into a corrected final gravity: FG = 1 − 0.0044993×OG_brix + 0.011774×FG_brix + 0.00027581×OG_brix² − 0.0012717×FG_brix² − 0.00000728×OG_brix³ + 0.000063293×FG_brix³. It is accurate for final gravities below about 1.014; above that it becomes unreliable, and independent tests rank it less accurate than a direct hydrometer reading.
How do I correct a hydrometer reading for temperature?
Hydrometers are calibrated at a specific temperature (usually 60°F / 15.6°C or 68°F / 20°C). If your sample is warmer, it reads low; if cooler, it reads high. Our lab uses the straighttothepint polynomial correction: corrected gravity = measured × (density factor at sample temp ÷ density factor at calibration temp). For example, 1.060 at 100°F on a 60°F hydrometer corrects to about 1.066. For hot wort, cool the sample below ~100°F first — correction error grows with temperature distance.
How do I know if my hydrometer is accurate?
Test it in distilled water at its calibration temperature: it should read exactly 1.000. If it reads 1.002, subtract 0.002 from every future reading; if 0.998, add 0.002. Also check that it floats freely without touching the cylinder walls, spin it to release CO₂ bubbles, and read the meniscus bottom at eye level. Hydrometers are fragile — a cracked or lead-ball-displaced hydrometer is silently wrong, not obviously broken.
What is the difference between Brix, Plato and specific gravity?
They are three scales for the same thing: dissolved sugar concentration. 1 °Plato ≈ 1 °Brix ≈ 4 gravity points (e.g., 12 °Plato ≈ 1.048 SG). Our converter handles all three: SG = (Brix ÷ (258.6 − ((Brix ÷ 258.2) × 227.1))) + 1. Plato is the brewer's standard in professional brewing; Brix is what refractometers display; specific gravity is what hydrometers read.
What are the standard, alternate and real-extract ABV formulas?
Standard: ABV = (OG − FG) × 131.25 — simple, fine under ~6%. Alternate (Ritchie): ABV = 76.08×(OG−FG) ÷ (1.775 − OG) × (FG ÷ 0.794) — better for high-gravity beers. Real-extract (Hall/Balling): computes real extract first, then ABV = ((OE − RE) ÷ (2.0665 − 0.010665×OE)) × 1.25 — most accurate across the widest range. Our agreement panel runs all three and flags how far apart they are.
What is apparent vs real attenuation?
Apparent attenuation = (OG − FG) ÷ (OG − 1) × 100. It looks like 75–80% for a typical beer, but it is 'apparent' because alcohol is lighter than water, making FG read lower than the true residual sugar. Real attenuation uses real extract (RE = 0.1808×OE + 0.8192×AE) and is about 20% lower — typically 60–65%. Yeast manufacturers quote apparent attenuation; real attenuation is the physically honest number.
Can I estimate ABV without knowing my original gravity?
Yes, approximately. If you only have final gravity, assume a typical apparent attenuation (75% for most ale yeasts): OG ≈ (FG − 0.75) ÷ 0.25, then ABV = (OG − FG) × 131.25. For FG 1.012 at 75% attenuation, that estimates OG 1.048 and 4.7% ABV. The result is an estimate, not a measurement — it shifts by about ±1% ABV for every 5 points of assumed attenuation, so use the style-based range we show.
How do I dilute a beer that is too strong or fix a missed OG?
To dilute: new gravity points = current points × current volume ÷ (current volume + water added), and new ABV = current ABV × volume ÷ (volume + water). Adding 0.5 gallon of water to 5 gallons of 1.052 beer drops it to about 1.047. To fix an undershot OG, add fermentable: pounds = points needed × gallons ÷ PPG (DME 44, LME 36, table sugar 46, dextrose 42, honey 38 PPG).
How many calories and standard drinks are in my beer?
Calories per 12 oz ≈ (6.9 × ABW + 4 × real extract) × 3.55, where ABW = ABV × 0.789 ÷ FG. A typical 5.4% ABV, FG 1.011 beer lands around 169 kcal per 12 oz. Standard drinks: US = 14 g alcohol, UK = 8 g, Australia = 10 g per standard drink; a 12 oz beer at 5.4% ABV is about 1.2 US standard drinks.
What is the wort correction factor for refractometers?
Handheld refractometers are calibrated for sucrose solutions, but wort contains mostly maltose, which bends light differently. Most wort reads about 4% high, so divide raw wort Brix readings by ~1.04 (the 'wort correction factor') before using them. You can determine your own factor by comparing your refractometer's OG reading against a trusted hydrometer — we include a field for it in the refractometer lab.
Why is my refractometer accurate for OG but not for FG?
For OG there is no alcohol yet, so the Brix reading (with the wort correction factor) converts cleanly to specific gravity. For FG, alcohol is present and distorts the reading, which is why you need the Terrill correction — and even then, the correction is an empirical fit. Best practice: use the refractometer for quick checks during fermentation, but confirm final gravity with a hydrometer.
Is homebrewing beer legal where I live?
It depends entirely on your jurisdiction. Homebrewing is legal at the federal level in the United States (up to 100 gallons per adult per year, 200 per household), broadly legal in the UK, EU, Australia and Canada for personal use, but restricted or illegal in some countries. Check your local laws before brewing, and never sell homebrewed beer without a commercial license — homebrewing is personal-use only almost everywhere.
What is the legal drinking age for the ABV results?
This calculator is an informational tool for adult homebrewers. The legal drinking age varies: 21 in the United States, 18 in most other countries (including the UK, EU, Australia, Canada), and differs elsewhere. The ABV figures here are estimates for recipe planning, not lab-grade measurements, and are no substitute for professional alcohol testing.
Is this calculator private? Where does my data go?
Every calculation happens entirely inside your browser. Your readings are never sent to any server, stored, or tracked — there is no account, no analytics on your inputs, and no external request. You can verify this by disconnecting from the internet after the page loads; everything keeps working.