Measurements and calculations
Gravity, alcohol, bitterness, colour and formulas. 20 terms.
Alcohol by volume (ABV)
- The share of alcohol in the finished beer, in percent by volume. It is calculated from original and final gravity: the more sugar the yeast ferments, the higher it is. The final-beer calculator shows it.
Apparent and real attenuation
- In finished beer the hydrometer reads too low because alcohol is lighter than water. So the apparent attenuation, calculated from original and final gravity, is higher than the real one. Recipes and yeast makers usually give the apparent value; the real one is about a fifth lower.
Attenuation
- How much of the extract the yeast has fermented. Usually 70–85 %, depending on yeast and beer style.
Brewhouse efficiency
- How much of the extract in the malt actually ends up in the wort. Usually 60–75 % on homebrew systems.
Brewing abbreviations
- OG = original gravity, FG = final gravity, SG = specific gravity, °P = degrees Plato, °Bx = Brix, ABV = alcohol by volume, IBU = international bitterness units, EBC and SRM = colour, RA = residual alkalinity, FWH = first wort hopping, BIAB = brew in a bag, DMS = dimethyl sulphide.
Brix (°Bx)
- Unit shown by a refractometer for sugar content. For wort, °Bx divided by 1.04 gives the true value (13.5 °Bx ≈ SG 1.053). After fermentation a correction is needed; the final-beer calculator does it for you.
BU:GU
- Ratio of bitterness (IBU) to gravity units (the last two digits of the SG). Around 0.5 tastes balanced, above 0.7 clearly bitter. The final-beer calculator shows it.
Calculating alcohol
- Alcohol follows from original and final gravity. Rule of thumb with SG: ABV ≈ (OG − FG) × 131. Example: 1.050 and 1.010 give about 5.2 % ABV. The final-beer calculator uses a more precise formula that also holds for strong beers.
Calculating beer colour (Morey)
- Malt amount, malt colour and wort volume give the malt colour units (MCU). Morey’s formula converts them to SRM: SRM = 1.49 × MCU to the power of 0.69, and EBC ≈ SRM × 1.97. The final-beer calculator does this automatically.
Calculating IBU (Tinseth)
- Bitterness depends on hop amount, alpha acid, boil time, wort volume and gravity: IBU ≈ utilisation × alpha acid × hops in mg per litre. Utilisation rises with boil time, reaching about 20–25 % after 60 minutes, and falls in strong wort. The final-beer calculator uses the Tinseth formula and also accounts for the whirlpool.
EBC
- Measure of beer colour (European Brewery Convention). The higher, the darker. EBC ≈ SRM × 1.97.
Final gravity
- The extract left after fermentation, measured with a hydrometer. Together with the original gravity it gives the alcohol content.
Hydrometer
- Floating instrument for measuring original and final gravity, usually calibrated to 20 °C (68 °F). A warmer sample reads slightly low.
IBU
- Measure of bitterness (International Bitterness Units). The site uses the Tinseth formula, including the whirlpool.
Original gravity (OG)
- Sugar content of the wort before fermentation. English-speaking brewers give it as specific gravity (SG), e.g. 1.048; in Europe it is often given in degrees Plato (12 °P ≈ SG 1.048). It determines how much alcohol the beer can have.
pH meter
- Measures mash pH more accurately than test strips. Calibrate it with buffer solutions (pH 4.0 and 7.0) before every brew day, cool samples to room temperature and always store the electrode moist in storage solution, never in distilled water.
ppm and mg/l
- For water both are practically the same: 1 mg/l equals 1 ppm (parts per million). Europe mostly uses mg/l, the US ppm. Hardness and alkalinity are often given as CaCO₃.
Refractometer
- Measures sugar content in °Brix from a few drops. For wort a correction factor of about 1.04 applies (13.5 °Bx ≈ SG 1.053). After fermentation alcohol distorts the reading; the calculator corrects for it.
Scaling a recipe
- A recipe can be scaled to any batch size. Malt, hops, water and yeast change in the same ratio; gravity, IBU, colour and temperatures stay the same. On this site the batch size calculator in every recipe does it for you.
Specific gravity (SG)
- Density of the wort compared with water (water = 1.000). Typical wort is around 1.040–1.060. Rule of thumb: the last two digits divided by 4 give roughly degrees Plato, so 1.048 ≈ 12 °P.