FireOps CalcFlow per line = Total Flow ÷ Number of active supply lines
Required PDP = Highest Line FL + Target Intake ± Elevation + Device Loss
Step-by-step process
Enter total target flowUse the water supply flow you need at the receiving engine.
Count active supply linesFor two lines, split the flow unless your department uses a different method or the lines are unequal.
Calculate each lineUse each hose size, length, and C-value.
Use the highest line lossThe supply engine must pump enough pressure to overcome the highest-loss supply path.
Maintain target intakeAdd the desired residual or intake pressure at the receiving engine.
Worked example
Total flow1000 GPM
Supply linesTwo 2½ inch lines
Flow per line500 GPM each
Target intake20 PSI
PDPHighest line FL + 20 PSI
This is the key difference from a nozzle line: water supply calculations need a manual Total Flow GPM field, not a nozzle GPM.
Common mistakes to avoid
- Using a default nozzle pressure that does not match the actual nozzle.
- Forgetting extra hose, elevation, or appliance loss.
- Using textbook coefficients when your department has known hose data.
- Treating a training estimate as a replacement for department SOPs or instructor direction.
How FireOps Calc helps
FireOps Calc is built to make this process faster on a phone. Open the web calculator, enter your hose, nozzle, flow, elevation, and appliance values, then review the math breakdown instead of only seeing a final number.
FAQ
What if the two supply lines are different lengths?
Calculate each line separately and use the highest pressure requirement.
Why do I need target intake pressure?
The supply engine should leave enough pressure at the receiving engine or appliance to maintain usable intake/residual pressure.