Original Gravity Calculator

How Original Gravity Is Calculated for Homebrew

Original Gravity (OG) measures the sugar content of wort before fermentation. It predicts potential alcohol content and helps you match your recipe to the target beer style.

Extract-Based OG Formula: OG = 1 + (PPG × Weight_lbs / Volume_gal) / 1000

Where PPG = points per pound per gallon (a measure of fermentable yield):

• Pale 2-row malt: 37 PPG (at ~75% efficiency)
• Crystal/caramel malt: 34 PPG
• Roasted barley: 25 PPG
• Dry malt extract (DME): 45 PPG
• Liquid malt extract (LME): 36 PPG

All-Grain with Mash Efficiency: OG = 1 + (Grain_lbs × Max_PPG × Efficiency% / Batch_gallons) / 1000

Worked Example: 5-gallon all-grain American Pale Ale, 75% mash efficiency:

• 10 lbs 2-row (max 37 PPG) → contribution = 10 × 37 × 0.75 = 277.5 points
• 0.5 lbs Crystal 40 (max 34 PPG) → contribution = 0.5 × 34 × 0.75 = 12.75 points
• Total gravity points = 290.25 / 5 gallons = 58.05 points
• OG = 1.058

Target OG by Style:

• American Light Lager: 1.028–1.040
• Pale Ale / IPA: 1.044–1.070
• Stout: 1.060–1.090
• Belgian Tripel: 1.075–1.085
• Barleywine: 1.080–1.120

Correcting Low OG: Add DME to raise gravity. Extract dissolves straight into the boil rather than going through the mash, so it yields close to its full 45 PPG rather than your mash efficiency: a quarter pound per gallon lifts the gravity by about 11 points, taking 1.050 to 1.061. That is worth knowing on brew day, because the correction is bigger than most people expect and it is easy to overshoot a hoppy beer into something syrupy.

Efficiency is the number that is actually yours. PPG comes off the maltster’s spec sheet and is close to fixed. Batch size is whatever your kettle holds. Efficiency is the only input here that describes your particular crush, mash tun, sparge technique and grain bill, and it is the reason two brewers following the same recipe land three gravity points apart.

Most homebrew systems run 65 to 75%. A BIAB setup with a fine crush often beats that; a cooler mash tun with a coarse crush from a homebrew shop mill often does not. Do not chase a published figure. Brew, measure, and use what you actually got, because a recipe scaled on someone else’s efficiency is a recipe for the wrong beer.

Three things that pull efficiency down, in the order worth checking:

• The crush. More surface area, more conversion. This is the single biggest lever and the cheapest to change.
• A big grain bill. Past about 1.070 the same system will lose several points, because there is more sugar left clinging to more grain. Recipes for strong beer usually assume this and you should too.
• Sparge volume and temperature. Rinsing too fast, too cold, or too little leaves sugar in the tun. Rinsing too far the other way drags tannins out with it.