U.S. Gallons per minute (gpm) x .1337 = Cubic feet per minute
Cubic feet per minute x 7.48 = U.S. gallons per minute
Cubic feet per second x 448.8 = U.S. gallons per minute
U.S. gallons per minute x 0.00223 = Cubic feet per second
Acre inches per hour x 453 = U.S. gallons per minute
British Imperial gallons x 1.201 = U.S. gallons
U.S. gallons x 0.833 = British Imperial gallons
Acre feet x 325,850 = U.S. gallons
Acre inches x 27154 = U.S. gallons
GPM x 226.8 = liters per hour
cubic feet per minute x 1699 = liters per hour
acre inches per hour x 1712.3 = liters per minute
acre feet x 1231.7 = cubic meters
acre inch x 102.64 = cubic meters
velocity (feet/second) x 0.3047 = velocity (meters/second)
velocity (meters/second) x 3.281 = velocity (feet/second)

Velocity in feet per second = (0.408 x GPM) / Inside diameter of pipe in inches, squared

Q=AV (quantity = area x velocity) ("the basic equation of water flow")
(example: quantity in cubic feet per second = square feet of area x feet per second velocity)

One inch of water depth = 0.62 gallons per square foot of area