TL;DR
Original Gravity (OG) is the specific gravity of your wort or must before yeast is pitched. It tells you how much fermentable sugar is dissolved in the liquid, which directly predicts your beer’s potential alcohol content. Typical OG for beer ranges from 1.030 (session ale) to 1.120+ (barleywine). Measure OG with a hydrometer or refractometer on brew day, correct for temperature, and pair it with Final Gravity to calculate ABV using the formula (OG − FG) × 131.25.
What Exactly Is Original Gravity?
Specific gravity (SG) compares the density of a liquid to pure water. Water at 20 °C (68 °F) has a specific gravity of 1.000. When you dissolve sugar in water — as happens when you mash grain or add honey to water — the liquid becomes denser. A wort with an SG of 1.050 is 5 % denser than water.
Original Gravity is simply the specific gravity measured at a specific moment: after the boil, after the wort is cooled, and before fermentation begins. It is the starting line for everything that follows.
OG matters because:
- It predicts ABV. Higher OG means more sugar for yeast to ferment, which means more alcohol.
- It tells you about recipe efficiency. If you expected 1.060 but got 1.048, your mash didn’t convert as well as planned.
- It guides yeast selection. High-gravity worts (1.080+) need robust yeast strains and possibly staggered nutrient additions.
- It’s a quality control checkpoint. Consistent OG across batches means your process is dialed in.
For a full explanation of how OG and Final Gravity work together in the ABV formula, see Abv Calculator Og Fg Explained.
How to Measure Original Gravity
Using a Hydrometer
The hydrometer is the traditional tool. Cool your wort to below 30 °C (86 °F), pull a 200 mL sample into a test jar, float the hydrometer, and read at the bottom of the meniscus. Correct for temperature if the sample isn’t at the hydrometer’s calibration temperature (usually 20 °C).
For a detailed walkthrough with photos and troubleshooting, head over to How To Use Hydrometer Measure Abv.
Using a Refractometer
A refractometer needs only 2–3 drops of wort on its prism. It reads in Brix (degrees of sugar concentration). To convert Brix to SG for an unfermented sample:
SG = 1 + (Brix / (258.6 − (Brix × 227.1 / 258.2)))
Or use the simplified approximation:
SG ≈ 1 + (Brix × 0.004)
A wort reading 12 °Bx is approximately SG 1.048.
The
Important: Refractometers are only directly accurate for unfermented wort. Once alcohol is present, the refractive index changes and you need a correction formula. That limitation doesn’t apply to OG readings since fermentation hasn’t started yet.
Using a Digital Hydrometer (Tilt, iSpindel)
Floating digital hydrometers transmit SG and temperature readings wirelessly to your phone. They’re excellent for monitoring fermentation in real time without opening the fermenter, and their initial reading serves as your OG.
Typical OG Ranges by Beer Style
Understanding where your target OG should land helps you design recipes and diagnose problems.
| Style | OG Range | Approx. ABV |
|---|---|---|
| Berliner Weisse | 1.028–1.032 | 2.8–3.8 % |
| English Mild | 1.030–1.038 | 3.0–3.8 % |
| Ordinary Bitter | 1.032–1.040 | 3.2–3.8 % |
| Wheat Beer (Hefeweizen) | 1.044–1.052 | 4.3–5.6 % |
| American Pale Ale | 1.045–1.060 | 4.5–6.2 % |
| Amber Ale | 1.045–1.060 | 4.5–6.2 % |
| Porter | 1.040–1.052 | 4.0–5.4 % |
| IPA | 1.056–1.070 | 5.5–7.5 % |
| Saison | 1.048–1.065 | 5.0–7.0 % |
| Stout (Dry) | 1.036–1.050 | 4.0–5.0 % |
| Belgian Tripel | 1.075–1.085 | 7.5–9.5 % |
| Imperial Stout | 1.075–1.115 | 8.0–12.0 % |
| Barleywine | 1.085–1.120 | 8.0–12.0 % |
| Mead (standard) | 1.090–1.120 | 10.0–14.0 % |
These ranges come from the 2021 BJCP Style Guidelines and represent the middle of the bell curve. Your exact OG depends on grain bill, mash efficiency, and water volume.
What Factors Affect OG?
1. Grain Bill and Extract Potential
Every malt and adjunct contributes a known amount of sugar per kilogram. Base malts like Pale Malt 2-Row yield approximately 36–37 points per pound per gallon (PPG), or about 1.037 SG when 1 lb is dissolved in 1 gallon. Crystal malts, roasted malts, and adjuncts each have their own extract potentials.
| Ingredient | PPG | Max SG (1 kg in 4 L) |
|---|---|---|
| Pale Malt 2-Row | 36–37 | 1.082 |
| Munich Malt | 34–35 | 1.077 |
| Crystal 60L | 33–34 | 1.075 |
| Wheat Malt | 36–37 | 1.082 |
| Table Sugar (Sucrose) | 46 | 1.102 |
| Honey | 32–38 | 1.072–1.086 |
| Dry Malt Extract (DME) | 44 | 1.098 |
| Liquid Malt Extract (LME) | 36 | 1.082 |
2. Mash Efficiency
Mash efficiency is the percentage of available sugar that actually ends up dissolved in your wort. A typical all-grain homebrewer achieves 65–78 % mash efficiency. Commercial breweries with optimised systems may hit 85–90 %.
Example: If your grain bill has a theoretical maximum OG of 1.070 and your mash efficiency is 72 %, your expected OG is:
OG = 1 + (0.070 × 0.72) = 1.050
3. Boil Volume and Evaporation
During the boil, water evaporates but sugar stays behind. A longer or more vigorous boil concentrates the wort and raises OG. Typical evaporation rate is 3.5–5 litres per hour (0.9–1.3 gallons per hour) for a standard homebrew kettle.
4. Water-to-Grain Ratio
Thicker mashes (less water per kilogram of grain) produce denser first runnings but may extract less efficiently. A typical ratio is 2.5–3.5 L/kg (1.2–1.7 qt/lb).
5. Sparging Technique
Fly sparging generally extracts more sugar than batch sparging. No-sparge (full-volume mash) methods are simpler but yield lower efficiency — often 55–65 %.
When Your OG Misses the Target
OG Is Too Low
| Possible Cause | Fix |
|---|---|
| Poor mash efficiency | Crush grain finer, extend mash 15 min, check mash pH (target 5.2–5.4) |
| Too much sparge water | Measure volumes precisely |
| Incorrect grain weight | Weigh, don’t estimate |
| Old or poorly stored grain | Buy from a supplier with high turnover |
Quick fix on brew day: Add dry malt extract (DME). Each 100 g of DME added to 20 L (5.3 gal) raises OG by approximately 0.002.
OG Is Too High
| Possible Cause | Fix |
|---|---|
| Over-concentrated wort (excess boil-off) | Add pre-boiled sterile water to hit target volume |
| Measured before full kettle was mixed | Stir thoroughly, then re-measure |
OG in Different Units
You’ll encounter several units across brewing literature:
| Unit | Example | Equivalent |
|---|---|---|
| Specific Gravity (SG) | 1.050 | — |
| Gravity Points | 50 | SG minus 1, times 1000 |
| Degrees Plato (°P) | 12.4 °P | ≈ SG 1.050 |
| Degrees Brix (°Bx) | 12.4 °Bx | ≈ SG 1.050 (pre-fermentation) |
For homebrewing purposes, Brix and Plato are nearly identical for unfermented wort. The divergence only becomes significant above 15 °Bx.
Plugging OG into the ABV Calculator
Once you’ve measured OG and your fermentation is complete, take a Final Gravity reading and use our calculator:
ABV CalculatorCalculate your alcohol by volume from gravity readings
The calculator applies the standard formula and handles unit conversions so you get an accurate ABV with minimal effort. For more context on how different beer styles land on the ABV scale, check out Homebrew Abv By Beer Style.
The Relationship Between OG and Body
OG doesn’t just predict alcohol — it also hints at the finished beer’s body and mouthfeel. A high OG wort fermented with a low-attenuating yeast will leave more residual sugar, giving a fuller, sweeter beer. The same OG fermented with a highly attenuating strain (like many Belgian yeasts) will finish dry and thin.
This is why OG alone doesn’t tell the whole story. You need to consider:
- Yeast attenuation (typical range 70–85 %)
- Mash temperature (higher mash temps = more unfermentable sugars = fuller body)
- Adjuncts (lactose, oats, and flaked barley add body regardless of fermentability)
Tracking OG Over Multiple Batches
Keeping a brew log with OG for every batch reveals patterns in your system. After 5–10 batches, you’ll know your typical mash efficiency precisely, which makes recipe formulation far more predictable.
Record at minimum:
- Date
- Recipe name
- Target OG vs. actual OG
- Pre-boil volume and gravity
- Post-boil volume and gravity
- Mash temperature and duration
- Any process notes
This simple habit is what separates consistent brewers from those who get a different beer every time.
Affiliate Disclosure
This article contains affiliate links. If you purchase through these links, we may earn a small commission at no extra cost to you. This helps support the site and allows us to keep creating free brewing resources. We only recommend products we have used or thoroughly researched.
Methodology
Gravity ranges and style parameters are drawn from the 2021 BJCP Style Guidelines (Beer Judge Certification Program). Extract potential values (PPG) reference Brewing Classic Styles by Jamil Zainasheff and John Palmer, and cross-checked with Briess Malt technical data sheets. Mash efficiency benchmarks are compiled from large-scale homebrew surveys conducted on HomeBrewTalk (2019, n=1,247). The SG-to-Brix conversion formula follows the work of Louis K. Bonham as published in Brewing Techniques (1997). Temperature correction data aligns with OIML R 44 tables for saccharometer calibration.