🌡️ Gravity Correction Calculator
Accurate gravity readings for any temperature or instrument
Get accurate gravity readings regardless of temperature or measurement method. This calculator corrects hydrometer readings for temperature and converts refractometer Brix readings to specific gravity.
📚 Understanding Gravity Corrections
Gravity measurements are affected by temperature and the presence of alcohol. This calculator ensures your readings are accurate regardless of these factors.
Why Corrections Are Needed:
- Hydrometers: Calibrated at a specific temperature (usually 60°F/15.6°C)
- Liquid density: Changes with temperature - warmer liquid is less dense
- Alcohol presence: Makes refractometer readings inaccurate after fermentation starts
- Accuracy matters: Small errors compound in ABV calculations
Hydrometer Temperature Correction:
Hydrometers are calibrated to be accurate at a specific temperature, typically 60°F (15.6°C). When you measure wort at a different temperature, you must correct the reading:
- Hot wort (above calibration): Reading is lower than actual gravity
- Cold wort (below calibration): Reading is higher than actual gravity
- At 80°F: Add ~0.002 to reading
- At 100°F: Add ~0.005 to reading
- At 40°F: Subtract ~0.002 from reading
Temperature Correction Formula:
Corrected SG = Measured SG + [(Sample Temp - Calibration Temp) × 0.00013]
This uses the polynomial approximation for water/wort density changes.
Best Practices for Hydrometer Readings:
- Cool your sample: Aim for calibration temperature (60°F)
- Remove bubbles: CO₂ bubbles make reading artificially high
- Spin the hydrometer: Releases trapped bubbles
- Read at eye level: Bottom of meniscus is the correct reading
- Clean hydrometer: Oil or residue affects buoyancy
- Wait for stability: Let sample settle before reading
- Temperature-adjust: Or wait for sample to reach 60°F
Refractometer Advantages:
- Small sample: Only need a few drops
- Quick reading: Results in seconds
- Temperature compensated: Many have ATC (Automatic Temperature Compensation)
- No need to cool: Can read hot wort (with ATC)
- Easy to use: Simple to read scale
Refractometer Pre-Fermentation:
Before fermentation, convert Brix to SG using:
SG = (Brix / (258.6 - (Brix × 0.8796))) × 1000
- Multiply by wort correction factor (typically 1.04)
- Test your refractometer with distilled water (should read 0 Brix)
- Calibrate against known gravity samples
Refractometer Post-Fermentation:
After fermentation starts, alcohol distorts refractometer readings. Use these correction formulas:
- Original Gravity: Convert OG Brix to SG using standard formula
- Final Gravity: Use alcohol-adjusted formula:
FG = 1.0000 - 0.0044993(OB) + 0.0117741(FB) + 0.000275806(OB²) - 0.00127169(FB²) - 0.0000727009(OB³) + 0.0000632929(FB³) - Where OB = Original Brix, FB = Final Brix
Wort Correction Factor:
Refractometers are calibrated for pure sucrose solutions, but wort contains complex sugars. The wort correction factor adjusts for this:
- Default: 1.04 (works for most beers)
- Find yours: Measure known gravity sample with both refractometer and hydrometer
- Calculate: WCF = Hydrometer SG / Refractometer SG
- Use consistently: Same WCF for all measurements from that refractometer
Brix to Specific Gravity Conversion:
Common Correction Scenarios:
You measure 1.050 at 85°F with a 60°F hydrometer
Correction: Add ~0.0025 = 1.0525 actual gravity
You measure 1.012 at 38°F with a 60°F hydrometer
Correction: Subtract ~0.002 = 1.010 actual gravity
OG was 14 Brix, current reading is 7 Brix
Actual FG: ~1.011 SG (not 1.028 if uncorrected!)
Hydrometer vs Refractometer:
- ✅ Accurate throughout fermentation
- ✅ No correction factor needed
- ✅ Inexpensive
- ❌ Requires large sample
- ❌ Must cool sample to calibration temp
- ❌ Fragile glass
- ✅ Tiny sample needed
- ✅ Quick readings
- ✅ Temperature compensated (ATC)
- ✅ Durable
- ❌ Needs alcohol correction post-fermentation
- ❌ More expensive
When to Use Each Method:
- Pre-fermentation OG: Either works great (refractometer is faster)
- During fermentation: Refractometer requires alcohol correction
- Final gravity: Hydrometer is simpler (no correction needed)
- Hot wort sampling: Refractometer with ATC is best
- Monitoring fermentation: Refractometer saves wort/beer
Calibrating Your Instruments:
Hydrometer:
- Test in distilled water at calibration temp (should read 1.000)
- If off, note the offset and adjust all readings
- Hydrometers can't be recalibrated - replace if significantly off
Refractometer:
- Place distilled water drop on prism
- Should read 0 Brix
- Adjust calibration screw if needed
- Determine wort correction factor with known samples
Accuracy Tips:
- Multiple readings: Take 2-3 readings and average
- Clean equipment: Residue affects accuracy
- Proper technique: Read at eye level, no parallax
- Calibrate regularly: Test instruments monthly
- Record temperatures: Always note sample temperature
- Degass samples: CO₂ throws off readings
Common Measurement Errors:
- Not cooling sample: 20°F difference = 0.003 SG error
- CO₂ bubbles: Makes gravity appear 0.002-0.005 higher
- Dirty instruments: Oil film affects buoyancy/refraction
- Wrong calibration temp: Using 68°F chart on 60°F hydrometer
- Parallax error: Reading from angle instead of eye level
- Not using alcohol correction: Refractometer FG will be way off
Advanced: Specific Gravity to Plato:
°Plato measures dissolved solids by weight. Convert SG to Plato:
°P = 259 - (259 / SG)
Or use: °P = (-1 × 616.868) + (1111.14 × SG) - (630.272 × SG²) + (135.997 × SG³)
- Plato and Brix are nearly identical for practical brewing
- Professional breweries often work in Plato
- Useful for extract efficiency calculations
Digital Tools:
Modern brewing includes digital options:
- Digital hydrometers: Display corrected gravity automatically
- Bluetooth hydrometers: Tilt, Rapt Pill - track fermentation continuously
- Digital refractometers: Show SG directly, some calculate FG
- These eliminate manual corrections but cost more