The unit used for water velocity in the head loss calculation is what?

• A. miles per hour
• B. feet per second
• C. kilometers per hour
• D. gallons per minute

Answer: (B)

In head loss calculations the velocity term appears as V^2/(2g). To keep the units consistent in US customary practice, velocity is expressed in feet per second. This matches g in feet per second squared and pipe lengths in feet, so the resulting head loss is in feet of water. Miles per hour or kilometers per hour are not the standard velocity units for these equations unless you first convert them to feet per second. Gallons per minute is a flow rate, not a velocity, so it doesn’t serve as the V term in the head loss formula. In SI, meters per second would be used, but for typical imperial-unit practice the correct velocity unit is feet per second.