Calculated Pump Duty Summary
Use these results for preliminary sizing only. Final pump selection should be checked against hydraulic calculations, code requirements, and manufacturer curves.
Project Inputs
Flow Analysis Graph
The chart compares sprinkler demand, hose allowance, total system demand, and the selected rated flow after applying safety margin.
Formula Used
- Sprinkler Flow (gpm) = Design Area × Density
- System Demand (gpm) = Sprinkler Flow + Hose Allowance
- Recommended Rated Flow (gpm) = System Demand × (1 + Safety Factor ÷ 100)
- Elevation Pressure (psi) = Elevation Rise ÷ 2.31
- Required Pump Pressure (psi) = Residual Pressure + Friction Loss + Elevation Pressure − Available Supply Pressure
- Rated Head (ft) = Required Pump Pressure × 2.31
- Water Horsepower = Rated Flow × Rated Head ÷ 3960
- Brake Horsepower = Water Horsepower ÷ Pump Efficiency
- Driver Horsepower = Brake Horsepower × (1 + Driver Service Margin ÷ 100)
How to Use This Calculator
- Select a hazard preset or keep the calculation fully custom.
- Enter the sprinkler design area and design density from your hydraulic basis.
- Add the expected hose allowance for sprinkler or hydrant demand.
- Enter residual pressure needed at the critical discharge point.
- Include elevation rise and total pipe friction loss to the remote point.
- Subtract the available supply pressure already present at the pump suction.
- Set pump efficiency and driver margin to estimate power requirements.
- Press Calculate Fire Pump Size to show results above the form, generate the graph, and enable CSV and PDF downloads.
Example Data Table
| Scenario | Design Area | Density | Hose Allowance | Safety Factor | Residual Pressure | Elevation Rise | Friction Loss | Supply Pressure | Rated Flow | Rated Head | Recommended Driver |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Warehouse example | 1500 ft² | 0.20 gpm/ft² | 500 gpm | 10% | 100 psi | 60 ft | 22 psi | 25 psi | 880 gpm | 284.1 ft | 125 HP |
Frequently Asked Questions
1) What does this calculator estimate?
It estimates sprinkler demand, hose allowance, required pump pressure, rated head, water horsepower, brake horsepower, and a suggested standard driver size. Use it for planning, budgeting, and early design comparisons.
2) Is the result the final pump selection?
No. Final pump selection should be checked against detailed hydraulic calculations, applicable fire codes, the authority having jurisdiction, suction conditions, and the actual manufacturer performance curve.
3) Why is hose allowance included?
Hose allowance represents additional firefighting demand beyond sprinkler flow. Including it helps size the pump for combined system demand instead of only the remote sprinkler area.
4) Why do elevation and friction matter?
Elevation rise increases the pressure required to reach the highest demand point. Friction loss accounts for pressure consumed by pipe, fittings, valves, and appurtenances along the flow path.
5) What is pump efficiency used for?
Pump efficiency converts hydraulic power into shaft power. Lower efficiency increases brake horsepower and usually leads to a larger motor or engine requirement.
6) What does driver service margin mean?
Driver service margin adds extra capacity above calculated brake horsepower. It helps cover real-world performance variation, aging, operating tolerances, and future adjustments.
7) Why can required pump pressure become zero?
If available supply pressure already covers the modeled residual, elevation, and friction losses, the simplified calculation may show zero added pump pressure. Review the full system carefully before concluding a pump is unnecessary.
8) Can I use hazard presets and still edit values?
Yes. Presets only fill common starting values. You can adjust every field afterward to reflect your project criteria, code basis, or hydraulic design sheets.