In the calibration jar method, how is the flow rate in gallons per minute (gpm) calculated?

• A. 15 Divided by S, Where S Is Seconds to Fill a 1-Quart Jar
• B. S Divided by 15
• C. 60 Divided by S
• D. S Divided by 60

Answer: (A)

In this method you measure how long it takes to fill a known volume, then convert that time to minutes and divide the volume by that time. The jar is 1 quart, which is 0.25 gallon. If S is the number of seconds to fill the jar, the time in minutes is S/60. The flow rate in gallons per minute is volume ÷ time, so 0.25 ÷ (S/60) = 0.25 × 60 / S = 15 / S. So the flow rate is 15 divided by the number of seconds to fill the jar. For example, if it takes 10 seconds, the flow rate is 15/10 = 1.5 gpm. The other options mis-handle the time units or the volume, leading to incorrect results.