Alcohol by Volume (ABV)

This formula estimates how much alcohol a fermentation has produced by comparing the liquid’s specific gravity before and after fermentation. Yeast consumes sugars, which lowers the density of the liquid; the drop in gravity is then converted into an approximate ethanol percentage using the factor 131.25. It is an empirical brewing rule of thumb, so it works well for typical beer and wine fermentations but can be less accurate for very strong, sweet, or unusual ferments.

Use this when you have hydrometer readings for the original and final gravity of a fermenting beverage and want a quick estimate of alcohol content. It is especially useful in homebrewing, winemaking, and basic food science measurements where precise laboratory alcohol analysis is not available.

• Subtracting in the wrong order and getting a negative value
• Using specific gravity readings that are not corrected for temperature
• Assuming this is an exact laboratory measurement rather than an estimate