1.0556
13.71
°P
1.0484
13.71
°P
5.5
%
1.0556
13.71
°P
1.0484
13.71
°P
5.5
%
Original gravity (OG) is one of the most fundamental measurements in homebrewing. It describes the density of your wort — the unfermented sweet liquid extracted from malted grain — relative to water, measured before fermentation begins. A higher original gravity means more fermentable sugars are present, which will produce more alcohol and typically a fuller-bodied, more complex beer. Understanding how to predict and measure original gravity is essential for recipe design, process control, and consistency across batches.
Gravity is measured on two scales: Specific Gravity (SG) and degrees Plato (°P). Specific gravity is a ratio — water has an SG of 1.000, and a typical wort might have an SG of 1.050, meaning it is 5% denser than water. The Plato scale, used predominantly by commercial breweries and in European brewing tradition, measures the percentage of sucrose equivalent by weight. These two scales are related by a polynomial conversion, and this calculator handles both directions of conversion.
Predicting original gravity before brewing requires knowing three things: the weight of your grain bill, the average extract potential of your malts, and your brewing efficiency. Extract potential is measured in Points Per Pound Per Gallon (PPG) — it describes how many gravity points (1 gravity point = 0.001 SG) one pound of malt would contribute to one gallon of wort if 100% of its sugars were extracted. Base malts like Pale Malt and Pilsner Malt typically have a potential of 37–38 PPG. Crystal malts and roasted malts generally contribute 28–35 PPG. Pure fermentable adjuncts like table sugar or corn sugar contribute 46 PPG.
Brewing efficiency is the percentage of available sugars you actually extract from the grain during the mashing and lautering process. All-grain homebrewers typically achieve 65–80% efficiency. Factors affecting efficiency include grain crush quality, mash temperature and time, water chemistry (pH), lautering speed, and equipment design. Most all-grain brewers target 70–75% efficiency as a baseline, and many homebrew recipe calculators default to 72–75%.
The estimated ABV range in this calculator is based on assuming 75% apparent attenuation — a typical value for most yeast strains fermenting a normal wort. More fermentable worts (lighter color, lower mash temperatures) or highly attenuating yeast strains can reach 80–85% apparent attenuation. Heavy, dark worts with lots of crystal malt may only attenuate to 65–70%. The ABV estimate here is therefore a useful guideline but should be refined using your specific yeast strain's attenuation data and a final gravity (FG) measurement after fermentation.
For extract brewers using malt extract (liquid or dry), the PPG values are higher (42–44 PPG for dry malt extract, 36–38 PPG for liquid malt extract) and efficiency is effectively 100% — all the fermentable sugars are already extracted. Simply set efficiency to 100% and adjust the PPG to match your extract type for accurate OG predictions.
The calculator converts grain weight from kilograms to pounds, then multiplies by the average PPG and efficiency to get total gravity points. These points are divided by the batch volume in gallons to get points per gallon (PPG/gal), then divided by 1000 and added to 1 to give specific gravity. Plato is calculated from SG using the standard polynomial equation: °P = -616.868 + 1111.14×SG - 630.272×SG² + 135.997×SG³. SG from Plato uses the simplified formula: SG = 1 + °P / (258.6 - (°P/258.2 × 227.1)).
Typical OG ranges: light session beers 1.030–1.040 (7.5–10 °P); standard ales and lagers 1.044–1.055 (11–13.5 °P); strong ales and IPAs 1.060–1.080 (15–19.5 °P); barleywines and imperial stouts 1.090–1.120 (21.5–28 °P). If your predicted OG is significantly higher or lower than intended, adjust grain weight proportionally. The estimated ABV range gives a rough target for finished beer strength, assuming 70–80% apparent attenuation.
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4.5 kg grain bill at 72% efficiency produces OG 1.053 (13.1 °P) in a 19-liter batch — a good target for an American Pale Ale. Expected ABV around 5.2% with standard attenuation.
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A commercial beer labeled at 14.5 °Plato (typical for a medium-strength European lager) corresponds to SG 1.059 — useful for style comparison or recipe targeting.
Specific gravity (SG) measures density relative to water — pure water = 1.000. Degrees Plato (°P) expresses the weight percentage of dissolved sugars equivalent to a sucrose solution of the same density. They measure the same thing but on different scales. Most homebrewing software and US-style brewing uses SG, while commercial brewing and German/Czech traditions use Plato. The conversion is a polynomial equation: approximately 1 °P ≈ 4 gravity points (e.g., 1.048 ≈ 12 °P).
The two standard instruments are: (1) a hydrometer — a glass float that sinks to a depth determined by liquid density, read at the liquid surface; inexpensive and accurate when temperature-corrected; (2) a refractometer — measures the bending of light through a small wort sample on a prism; very convenient, requiring only a few drops of wort. Note that refractometers give inaccurate readings after fermentation begins (alcohol affects the refractive index) and require a correction factor.
PPG stands for Points Per Pound Per Gallon — the maximum gravity points that one pound of a malt contributes to one gallon of water, assuming 100% extraction efficiency. This value is found in the maltster's product specifications, in homebrew ingredient databases (like Brewer's Friend or BeerSmith's grain database), or in homebrew reference books. Base malts typically range 36–38 PPG; specialty malts 28–35 PPG; pure sugars 44–46 PPG.
Efficiency has a direct proportional effect on OG. If you expect 72% efficiency but only achieve 65%, your OG will be 65/72 = 90% of your target — roughly 10% lower. Common causes of low efficiency include: coarse crush (not enough grain surface area exposed), incorrect mash pH, too short mash time, too rapid sparge, or channeling in the grain bed during lautering. Consistent efficiency develops with practice and good process control.
General targets: Session beers (3–4% ABV) OG 1.030–1.044; Standard ales/lagers (4–5.5% ABV) OG 1.045–1.060; Strong ales and IPAs (6–8% ABV) OG 1.060–1.080; Barleywines and imperial stouts (9–12%+ ABV) OG 1.090–1.120+. The Beer Judge Certification Program (BJCP) style guidelines specify OG ranges for every recognized beer style as a reference for recipe design.
The most common reasons: (1) different actual mash efficiency than assumed; (2) incorrect volume measurement (lower volume concentrates sugar, raising OG); (3) significant gravity sample not taken at correct temperature (hydrometers are calibrated at 60°F/15.6°C — apply temperature correction for hot wort); (4) grain crush quality variation. After a few brews, dial in your personal efficiency figure for more accurate predictions.
Yes. For liquid malt extract (LME), use PPG = 36–37 and efficiency = 100%. For dry malt extract (DME), use PPG = 42–44 and efficiency = 100%. For partial mash (combining grain mashing with malt extract), calculate the grain contribution at your mash efficiency and the extract contribution at 100%, then combine the total gravity points and divide by batch volume in gallons.
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