Which statement best describes GPM vs PSI?

• A. GPM measures pressure, PSI measures flow
• B. GPM and PSI are the same quantity
• C. GPM measures flow rate and PSI measures pressure
• D. PSI measures temperature

Answer: (C)

Flow rate versus pressure: GPM stands for gallons per minute and tells you how much water is moving through the system each minute. PSI stands for pounds per square inch and tells you the force pushing that water through pipes and emitters. In irrigation, you need both: a system must deliver enough water (GPM) and have enough push (PSI) to overcome resistance in pipes and sprinkler heads. Knowing one alone doesn’t tell you the other, so the correct description is that GPM measures flow rate and PSI measures pressure. The other statements mix up what each quantity represents, imply they’re the same, or bring in temperature, which isn’t related to these two measurements.