A gallons per hour (GPH) calculator is a tool used to determine the volume of fluid that passes through a particular point in one hour. It quantifies the speed of flow in a standardized unit. Whether you are a hobbyist or a professional, this calculator provides critical information. For example, an aquarist uses it to ensure their aquarium filter has the correct GPH rating to keep the water clean and the fish healthy. Similarly, a boat owner might use it to calculate the GPH of their engine to estimate fuel needs for a trip. The calculator takes simple inputs—typically a volume of liquid and the time it took to move that volume—and provides the flow rate in GPH, making it easy to compare pumps, check system efficiency, or plan resource usage.
formula
The most direct way to calculate gallons per hour is by using a simple formula that relates volume and time. You use this when you can measure the total amount of liquid that has moved over a specific duration.
GPH = Total Gallons / Total Hours
To use this formula, you simply measure the total volume in gallons that has been transferred and divide that number by the total time in hours it took for the transfer to complete. The result is your flow rate in GPH. If your time is measured in minutes or seconds, you must first convert it to hours before using the formula.
Common Flow Rate Conversions
Often, you may need to convert GPH to other units of flow rate, or vice versa. This table provides quick conversions for some common GPH values, which can be helpful for comparing specifications on different equipment.
| Gallons Per Hour (GPH) | Gallons Per Minute (GPM) | Liters Per Hour (LPH) | Liters Per Minute (LPM) |
| 1 | 0.017 | 3.785 | 0.063 |
| 10 | 0.167 | 37.85 | 0.631 |
| 50 | 0.833 | 189.25 | 3.154 |
| 100 | 1.667 | 378.5 | 6.309 |
| 500 | 8.333 | 1892.5 | 31.541 |
| 1000 | 16.667 | 3785.0 | 63.083 |
Example
Let's walk through a practical example. Imagine you want to find the GPH of the pump for your garden pond. You can do this by measuring how long it takes to fill a container of a known size.
- Get a container with a known volume, for instance, a 5-gallon bucket.
- Direct the pump's outlet hose into the bucket and start a stopwatch at the same time.
- Stop the watch as soon as the bucket is full. Let's say it took 30 seconds to fill the 5-gallon bucket.
Now, we need to calculate the GPH. First, we must convert our time from seconds to hours.
- There are 60 seconds in a minute and 60 minutes in an hour, so there are 3600 seconds in an hour (60 * 60).
- Time in Hours = 30 seconds / 3600 seconds/hour = 0.00833 hours
Next, we use the GPH formula:
GPH = Total Gallons / Total Hours
GPH = 5 gallons / 0.00833 hours
Finally, you perform the division:
GPH = 600.24
So, the pump for your garden pond has a flow rate of approximately 600 GPH.
Most Common FAQs
GPH is a critical specification for any pump because it tells you how much work the pump can do. For applications like aquarium filters or pond circulation, you need a pump with a GPH rating that is high enough to turn over the entire volume of water several times per hour to ensure adequate filtration and oxygenation. Choosing a pump with the wrong GPH can lead to poor system performance, whether it's a dirty fish tank or an inefficient water feature.
Converting Gallons Per Minute (GPM) to Gallons Per Hour (GPH) is very simple. Since there are 60 minutes in an hour, you just multiply the GPM value by 60 to get the equivalent GPH. For example, a pump rated at 10 GPM would have a flow rate of 600 GPH (10 * 60 = 600).
The rated GPH of a pump is usually its maximum possible output under ideal conditions, with no resistance. In a real-world application, the actual GPH will almost always be lower. Factors like the height the pump has to push the water (known as "head height"), the length and diameter of the tubing, and the number of turns or fittings in the plumbing all create resistance and will reduce the final flow rate.