About this tool
The Mash Efficiency & Expected OG Calculator links your grain bill, batch volume, and mash efficiency so you can either predict the original gravity you'll hit or work out the efficiency you actually achieved. It works from each fermentable's extract potential in PPG — points per pound per gallon, the gravity points one pound of that ingredient adds to one gallon at 100% extraction. Enter up to three fermentables with their weights and PPG values. Everything is computed locally in your browser.
Each fermentable contributes PPG × weight (in pounds) gravity points; the tool sums them to a total potential. In forward mode the predicted gravity points are total × efficiency ÷ batch volume (gallons), and the original gravity is OG = 1 + points / 1000. In reverse mode it takes your measured OG, converts it to points, and solves efficiency = measured_points × volume ÷ total_potential × 100. Metric weights (kg) are converted to pounds (× 2.20462) and metric volume (L) to gallons (÷ 3.78541), while PPG stays on its standard points/lb/gal scale. Typical PPG values: base malt ≈ 37, wheat ≈ 38, crystal ≈ 34, corn sugar ≈ 46, DME ≈ 44, honey ≈ 35.
As a worked example, 10 lb of base malt (37 PPG) into a 5.5-gallon batch at 72% efficiency gives 10 × 37 = 370 potential points, so 370 × 0.72 ÷ 5.5 ≈ 48.4 points, an OG near 1.048. The maximum possible OG at 100% extraction is also shown as a reference. Use pre-boil volume for mash efficiency and into-fermenter volume for brewhouse efficiency; for mixed grain bills enter each fermentable, or use a weighted-average PPG.