Original Gravity (Recipe) Calculator
Predict original gravity from your grain bill, mash efficiency and batch size.
Brewhouse efficiency, typically 65–80%
Grain bill
OG ≈ -
Original extract (°Plato)-
How it works
Predicted original gravity is the sum of each fermentable’s extract potential, scaled by how efficiently your system converts and extracts that potential, then spread across the batch volume.
OG points = Σ(PPG × weight_lb) × efficiency / volume_gal
OG = 1 + OG points / 1000
Sources: extract-potential math as documented by Brewer's Friend; John Palmer, How to Brew §2.
Estimates for planning. Actual OG depends on your real efficiency, crush, and volume measurement - confirm with a calibrated hydrometer or refractometer.
Frequently asked questions
- How is original gravity (OG) predicted from a grain bill?
- Each fermentable contributes gravity points equal to its extract potential (PPG, points per pound per US gallon) times its weight in pounds. Sum those, multiply by your mash/brewhouse efficiency, divide by the batch volume in gallons, and you have the predicted OG points. Add 1.0xx and that is your OG.
- What PPG should I use for my malts?
- PPG is the maximum gravity points one pound of the fermentable yields in one gallon at 100% extraction. Pale/base malts are around 36–37, crystal/caramel malts about 34–36, and pure sugars near 46. Use the maltster spec sheet when you have it.
- Why does efficiency matter so much?
- Efficiency captures how much of the grain’s potential sugar you actually extract and get into the kettle. Typical all-grain brewhouse efficiency is 65–80%. A 5-point swing in efficiency shifts OG by several points, so dial it in from past brews for accurate predictions.