How do you calculate original gravity from a grain bill?
Every fermentable has an extract potential — how many gravity points a pound gives a gallon of water if you got every last sugar out (37 for most pale malt, 44 for dry extract, 46 for pure sugar). Multiply weight by potential, add up the bill, take your brewhouse efficiency's share of it, and spread it over the volume that reaches the fermenter:
OG points = Σ (weight × potential) × efficiency ÷ batch volume
In pounds, PPG and gallons — or in kg, points-per-kg-per-liter (PPG × 8.35) and liters. Same equation, no apology needed.
So 11 lb of pale malt (37 PPG) and 1 lb of crystal (34) is 441 potential points; at 72 % efficiency into 5.5 gal that's an expected 1.058. The metric mirror — 5 kg pale, 0.45 kg crystal, 72 %, 21 L — lands at 1.057. Extract and sugar skip the efficiency step: they dissolve completely, so 1 lb of DME in a gallon is 1.044 whether your mash tun is good or not.
Extract potential of common malts and sugars
Rounded reference values; real lots vary a point either way, and a maltster's analysis sheet beats any table. Specialty malts contribute less than base malt, roasted grains least of all.
| Fermentable | PPG (per lb per gal) | PKL (per kg per L) | Color °L | Mashed? |
|---|---|---|---|---|
| Pale malt, 2-row | 37 | 309 | 2 | Yes — × efficiency |
| Pilsner malt | 37 | 309 | 2 | Yes — × efficiency |
| Maris Otter / pale ale malt | 38 | 317 | 3 | Yes — × efficiency |
| Vienna malt | 36 | 300 | 4 | Yes — × efficiency |
| Munich malt | 35 | 292 | 9 | Yes — × efficiency |
| Wheat malt | 38 | 317 | 2 | Yes — × efficiency |
| Crystal / caramel (10–120 °L) | 34 | 284 | 10–120 | Yes — × efficiency |
| Carapils / dextrine malt | 33 | 275 | 2 | Yes — × efficiency |
| Chocolate malt | 28 | 234 | 350 | Yes — × efficiency |
| Roasted barley | 25 | 209 | 300 | Yes — × efficiency |
| Black patent malt | 25 | 209 | 500 | Yes — × efficiency |
| Flaked oats | 33 | 275 | 1 | Yes — × efficiency |
| Flaked wheat / barley | 35 | 292 | 2 | Yes — × efficiency |
| Flaked corn / rice | 37 | 309 | 1 | Yes — × efficiency |
| Dry malt extract (DME) | 44 | 367 | 4 | No — counts at 100 % |
| Liquid malt extract (LME) | 36 | 300 | 4 | No — counts at 100 % |
| Table sugar / candi sugar | 46 | 384 | 0 | No — counts at 100 % |
| Corn sugar (dextrose) | 42 | 351 | 0 | No — counts at 100 % |
| Honey | 35 | 292 | 1 | No — counts at 100 % |
Fine-grind, dry-basis maxima in the ranges published by Palmer (How to Brew) and Daniels (Designing Great Beers); colors in °Lovibond from MoreBeer's malt chart. The calculator's dropdown uses these; pick "Other" to enter your maltster's figure. The color column feeds the beer color calculator.
How much grain do I need for a target OG?
Run the equation backwards. On the default profile — 5.5 gal at 72 % — a 1.050 beer needs 10.3 lb of pale malt; 20 L at 72 % needs 4.5 kg. The table below is base malt only, for the efficiencies most home systems actually get; the calculator's "target OG" mode uses your own numbers.
| Target OG | lb per 5 gal at efficiency | kg per 20 L at efficiency | |||||||
|---|---|---|---|---|---|---|---|---|---|
| 65% | 70% | 75% | 80% | 65% | 70% | 75% | 80% | ||
| 1.040 | 8.3 | 7.7 | 7.2 | 6.8 | 3.99 | 3.70 | 3.45 | 3.24 | |
| 1.045 | 9.4 | 8.7 | 8.1 | 7.6 | 4.48 | 4.16 | 3.89 | 3.64 | |
| 1.050 | 10.4 | 9.7 | 9.0 | 8.4 | 4.98 | 4.63 | 4.32 | 4.05 | |
| 1.055 | 11.4 | 10.6 | 9.9 | 9.3 | 5.48 | 5.09 | 4.75 | 4.45 | |
| 1.060 | 12.5 | 11.6 | 10.8 | 10.1 | 5.98 | 5.55 | 5.18 | 4.86 | |
| 1.065 | 13.5 | 12.5 | 11.7 | 11.0 | 6.48 | 6.01 | 5.61 | 5.26 | |
| 1.070 | 14.6 | 13.5 | 12.6 | 11.8 | 6.98 | 6.48 | 6.05 | 5.67 | |
| 1.075 | 15.6 | 14.5 | 13.5 | 12.7 | 7.47 | 6.94 | 6.48 | 6.07 | |
| 1.080 | 16.6 | 15.4 | 14.4 | 13.5 | 7.97 | 7.40 | 6.91 | 6.48 | |
| 1.090 | 18.7 | 17.4 | 16.2 | 15.2 | 8.97 | 8.33 | 7.77 | 7.29 | |
Pale malt at 37 PPG, all-grain. Scale linearly for other volumes (11 gal is 2.2× the 5-gal column). Extract: divide the potential points by 44 (DME) or 36 (LME) with no efficiency at all.
Brewhouse efficiency or mash efficiency — which number goes in?
Brewhouse efficiency — the number in your equipment profile — counts every loss from grain to fermenter: conversion, lautering, kettle trub, transfer. Mash (or lauter) efficiency counts only what made it into the kettle, so it's always higher, and a calculator that asks for "wort collected" wants that one. This page divides by the volume into the fermenter, so it wants brewhouse efficiency; if you only know a mash number, it will overpredict your OG by the kettle-loss share (typically 3–6 points).
From your last brew, not from a chart. Measure OG and volume into the fermenter, divide the points you got by the points the bill promised — that is your brewhouse efficiency. Guess 72 % for the first batch, then write down what actually happened. Brew Day will do this arithmetic and offer to save the result to your profile, so the next prediction is built on your kettle, not an average one.
Why did I miss my expected OG?
Two things move the answer, and one of them gets blamed far more than it deserves. Around a 1.050 target on the default profile:
| What went differently | Effect on OG |
|---|---|
| Efficiency 5 % lower than you thought | −3.5 points |
| Efficiency 5 % higher | +3.5 points |
| 0.5 gal / 2 L more wort than planned | −4.2 points |
| 0.5 gal / 2 L less wort than planned | +5.0 points |
| 1 lb / 0.45 kg of base malt left out | −4.8 points |
Base-malt-only 1.050 bill, 5.5 gal / 20.8 L at 72 %, from this page's engine.
One percent of efficiency is worth about 0.7 points at this gravity. Half a gallon of extra wort — a generous sparge, a short boil, a rinse of the kettle — costs 4.2 points, the same as 6% of efficiency. Before you lower the efficiency in your profile because you missed by four points, measure the volume that reached the fermenter. Half the "my efficiency dropped" stories are really "I collected more wort".
Pre-boil gravity: the reading that tells you early
Sugar doesn't appear or disappear in the boil — the same points just sit in fewer liters afterwards. So the pre-boil gravity your equipment profile predicts (for the example bill, 1.048 in 7.2 gal / 27.3 L of cooled wort) is a checkpoint you can hit while there's still time to act: low, and you can boil longer or add extract; high, and you can dilute or shorten the boil. Take the sample after the runoff is fully mixed, cool it, correct it for temperature, and compare. Miss the pre-boil number and the OG is already decided — everything after is just confirmation.