What Is the Gallons Per Hour (GPH) Calculator?
Gallons per hour (GPH) is a measure of volumetric flow rate — how many gallons of liquid pass a point, fill a tank, or are consumed in one hour. This calculator divides a known volume in gallons by the time in hours to give you the average flow rate. It is handy for pumps, fuel burn, irrigation, water heaters, aquariums, and any situation where you need a steady rate from a total amount.
How to Use It
Enter the total volume in gallons and the time it took in hours, then read the GPH result. The calculator also converts the answer to gallons per minute (GPM) for convenience. If your time is in minutes, divide by 60 first (for example, 30 minutes = 0.5 hours).
The Formula Explained
The equation is simply GPH = Volume ÷ Time. Volume is the number of gallons and time is the number of hours. Because it is a rate, the units cancel to gallons per hour. To get GPM, divide the GPH by 60, since there are 60 minutes in an hour.
$$\text{GPH} = \frac{\text{Volume (gallons)}}{\text{Time (hours)}}$$
Worked Example
Suppose a pump moves 500 gallons of water in 10 hours. Then $$\text{GPH} = 500 \div 10 = 50 \text{ gallons per hour}.$$ Converting to GPM: \(50 \div 60 \approx 0.83\) GPM. So the pump averages about 50 gallons every hour, or roughly 0.83 gallons each minute.
FAQ
Can I use minutes instead of hours? Convert minutes to hours by dividing by 60, then enter the result. For example, 45 minutes = 0.75 hours.
What if the time is zero? Flow rate is undefined when time is zero, so the calculator returns 0 — enter a positive time value.
How do I convert GPH to liters per hour? Multiply GPH by 3.78541 to get liters per hour (US gallons).
