Water Flow Rate Calculator

About the Water Flow Rate Calculator

This water flow rate calculator converts a measured water volume and elapsed time into gallons per minute, liters per minute, gallons per hour, liters per hour, and projected daily volume. It can also estimate the water cost for the measured volume.

Formula and assumptions

Gallons per minute = measured gallons ÷ minutes. Liters per minute = gallons per minute × 3.78541. Gallons per hour = gallons per minute × 60. Daily volume = gallons per minute × 1,440 minutes. Measured water cost = gallons ÷ 1,000 × price per 1,000 gallons.

Worked example

If 50 gallons are collected in 5 minutes, the flow rate is 10.00 gallons per minute, or 37.85 liters per minute. That equals 600 gallons per hour and 14,400 gallons per day if the flow continues continuously. At $4 per 1,000 gallons, the measured volume costs about $0.20 before the $75 testing or installation input.

Measurement checklist

• Use a container with a known and reliable volume.
• Start and stop timing consistently.
• Repeat the test and compare readings.
• Record pressure, pump setting, valve position, and elevation.
• Use peak and average flow appropriately for equipment sizing.

Manual calculation steps

1. Measure volume in gallons.
2. Measure elapsed time in minutes.
3. Divide gallons by minutes for GPM.
4. Multiply GPM by 60 for GPH.
5. Multiply GPM by 3.78541 for LPM.
6. Multiply GPM by 1,440 for daily gallons.

Common mistakes

• Using container capacity instead of actual collected volume.
• Timing too short for a fluctuating flow.
• Confusing pressure with flow rate.
• Using daily projections when the source is intermittent.

Frequently asked questions