About the Flow Rate Calculator
What is the Flow Rate Calculator?
This flow rate calculator gives two ways to find flow: time how long a bucket takes to fill, or multiply a pipe's cross-section by the water velocity.
Results are shown in every common unit – litres per second and per minute, cubic metres per hour, litres per day and US gallons per minute.
How to use the Flow Rate Calculator
- Method (sample: Bucket test – volume and time)
- Volume Collected (litres) (sample: 20)
- Time Taken (seconds) (sample: 12)
- Pipe Inner Diameter (mm) (sample: 25)
- Flow Velocity (m/s) (sample: 1.5)
- Press Calculate Flow Rate (results also refresh as you type). The result card shows the Flow Rate, along with Litres per second, Cubic metres per hour, Litres per day and US gallons per minute.
Formula used
Q = Volume ÷ Time; Q = (π ÷ 4) × D² × v
- D = pipe inner diameter
- v = flow velocity
1 m³/h = 16.67 L/min = 4.4 US GPM.
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| Method | Bucket test – volume and time |
| Volume Collected (litres) | 20 |
| Time Taken (seconds) | 12 |
| Pipe Inner Diameter (mm) | 25 |
| Flow Velocity (m/s) | 1.5 |
| Result | Value |
|---|---|
| Flow Rate | 100 L/min |
| Litres per second | 1.6667 L/s |
| Cubic metres per hour | 6 m³/h |
| Litres per day | 1,44,000 L |
| US gallons per minute | 26.42 GPM |
Tips for using the Flow Rate Calculator
- Repeat the bucket test three times and average the results.
- Use the inner diameter of the pipe, not the nominal size.