Calculator Inputs
Example Data Table
| Scenario | Hazard | Density | Area | Hose Allow. | Duration | Typical Outcome |
|---|---|---|---|---|---|---|
| Office Block | Light | 0.10 gpm/ft^2 | 1500 ft^2 | 100 gpm | 60 min | ~250 gpm sprinkler total |
| Retail / Light Storage | Ordinary 2 | 0.20 gpm/ft^2 | 1500 ft^2 | 250 gpm | 90 min | ~550 gpm sprinkler total |
| Industrial Process | Extra 1 | 0.30 gpm/ft^2 | 2500 ft^2 | 500 gpm | 120 min | ~1250 gpm sprinkler total |
Formula Used
- Sprinkler Demand = Design Density × Design Area
- Sprinkler Total = Sprinkler Demand + Hose Allowance + Standpipe
- Governing (with margin) = max(methods) × (1 + Safety %)
- Ci = 18 × F × √A (rounded to nearest 250)
- NFF = (Ci) × (O) × (1 + (X + P))
- Final rounding: 250 steps (over 2500 uses 500 steps)
- Base Volume = Governing Flow × Duration
- Adjusted Volume = Base ÷ (1 − Unusable%) × (1 + Reserve%)
- Hydraulic HP = (Flow × Pressure) ÷ 1714
- Brake HP = Hydraulic HP ÷ (Efficiency%)
How to Use This Calculator
- Select units and decide which method should govern.
- For sprinklers, choose a hazard and confirm density and area.
- Set hose and optional standpipe allowances to match your scenario.
- For hydrants, enter effective area and ISO factors if applicable.
- Choose a duration, then review storage and pump estimates.
- Download CSV/PDF to share with design and review teams.
Determine the governing flow rate
Fire-water demand typically starts with a sprinkler density multiplied by a remote design area, then adds hose and any standpipe allowance. Use the unit switch to work in gpm or L/min, and keep density and area consistent with the selected basis for comparison across teams. This calculator also lets you compare that sprinkler-based value with an ISO-style hydrant flow estimate for the same site. In combined mode, the larger flow becomes the planning target, then a safety margin is applied to reduce undersizing risk.
Set realistic durations for storage
Storage sizing is driven by duration as much as by flow. A 10% increase in minutes increases the base volume by 10%. Example: 750 gpm for 90 minutes equals 67,500 gallons before adjustments. The tool converts governing flow into a minimum tank volume using flow times duration, then adjusts for unusable volume and reserve or freeboard. This supports early budgeting and footprint checks.
Understand ISO fire flow inputs
For hydrant demand, the ISO method links effective floor area to required fire flow through construction and occupancy factors. Effective area should reflect the portion of the building that could be involved at one time, such as the largest compartment or wing. Exposure and communicating openings can increase the result when adjacent hazards or openings are present.
Translate demand into pump selection
Once the target flow is known, pump sizing must also consider the required pressure rise at the pump discharge. The calculator estimates pump power from flow and pressure, then adjusts for efficiency to approximate brake horsepower or kilowatts. Treat this as a preliminary value; final selection should use full hydraulic calculations, suction conditions, and manufacturer curves.
Document assumptions for review
Reviewers focus on assumptions: hazard class, density, design area, hose allowance, and duration. Exporting results to CSV or PDF keeps a consistent record for coordination, cost estimating, and permit submittals. When inputs change, rerun scenarios and keep the latest exports with the date and revision notes.
FAQs
1) Should sprinkler and hydrant demands be added together?
Usually they are not simply summed. Many projects choose the governing case based on the design basis and authority requirements. This calculator defaults to the maximum of the selected methods, with an optional safety margin.
2) Why is there a hose stream allowance?
Hose streams represent additional flow that may be expected during firefighting. Allowances vary by hazard and guidance. Use the auto option for typical values, then confirm the requirement for your jurisdiction and project type.
3) What does “unusable volume” mean for tanks?
Not all stored water is practically available due to dead storage, vortexing limits, suction losses, or low-level cutoffs. The unusable percentage inflates the tank size so the usable portion can still satisfy the required duration.
4) When should I use the ISO method?
The ISO approach is often used for planning hydrant fire flow where building construction, occupancy, exposures, and openings influence the estimate. It is helpful for early utility discussions, but it may not replace code-mandated fire flow criteria.
5) Are metric results calculated directly in metric?
Inputs are accepted in metric, converted internally to a consistent calculation basis, and then converted back for display. This keeps the formulas consistent while still letting teams work in L/min, m2, kPa, and liters.
6) Can I use these results for final design?
Use the outputs for planning and budgeting only. Final fire protection design should be verified by qualified professionals using applicable standards, hydraulic modeling, site supply tests, and the authority having jurisdiction.