This reference manual provides a list of approximately 4,400 unit conversion factors useful to Environmental Engineers (and probably others). It includes common conversions, such as feet to meters, miles to feet, and gallons to liters, but it also includes more obscure units that show up in old reports, old land surveys, and historic site records, such as chains and links (Gunter's and Ramden's), barns, perches, quintals, and ares. The book provides conversions for each unit to a variety of other units and back again with direct multiplier factors.