Illinois Fire Apparatus Engineer (FAE) Practice Exam 2026 - Free FAE Practice Questions and Study Guide

One gallon of water weighs approximately 8.35 pounds at its maximum density, which occurs at 39.2 degrees Fahrenheit (4 degrees Celsius). This value is widely recognized and used in various fields, including firefighting and engineering, where accurate calculations regarding fluid dynamics and weight are crucial for operations involving water and other liquids.

The weight of a gallon of water can vary slightly with temperature and impurities; however, the standard used in most practices and calculations remains 8.35 pounds. This value is essential for firefighters to understand when calculating water flow rates, pump capacities, and weight considerations for apparatus and storage.