FireOpsCalcHydrant Flow Calculator
Estimate available fire hydrant GPM from static pressure, residual pressure, measured flow, target residual pressure, or pitot pressure for firefighter training and preplanning.
Hydrant test inputs
Training/reference aid only. Follow department SOPs, applicable hydrant testing standards, instructor direction, and local water-system requirements.
Estimated hydrant flow
How to estimate available hydrant GPM
A hydrant flow test compares static pressure before water is flowing with residual pressure while water is flowing. Using the measured test flow, those values can be used to estimate how much water may be available at a selected target residual pressure.
Formula used: Flow × ((Static − Target Residual) ÷ (Static − Residual))0.54.
Static vs. residual pressure
- Static pressure is the pressure in the water system before the test outlet is flowing.
- Residual pressure is the pressure remaining while the hydrant is flowing during the test.
- Measured flow is the GPM produced during the test and becomes the baseline for estimating additional available flow.
Using pitot pressure to estimate outlet GPM
If measured GPM is not already known, select the pitot option and enter outlet diameter, pitot pressure, and discharge coefficient. The calculator estimates outlet flow using the standard pitot relationship shown in the results breakdown.
Hydrant flow calculator questions
What is a hydrant flow test used for?
Hydrant flow testing helps estimate available water supply for fire protection, preincident planning, system evaluation, and training. Local procedures and applicable standards should control how official tests are performed and documented.
Why use a target residual pressure?
The target residual lets you estimate available flow while preserving a selected pressure in the water system rather than assuming the system can be drawn down to zero pressure.
Can I calculate GPM from pitot pressure?
Yes. With outlet diameter and an appropriate discharge coefficient, pitot pressure can be used to estimate the GPM flowing from an outlet. This page includes that calculation option.
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