Fire & Safety Calculators
Standards-based fire alarm and fire-fighting calculators — NFPA 72, 13, 20 and 291. Each tool shows the formula, a worked example and a PDF report.
7 Calculators · Fire alarm & fire fighting (NFPA)
Fire Alarm & Detection (NFPA 72 / BS 5839)
Fire Fighting & Suppression (NFPA 13 / 20 / 291)
About Our Fire & Safety Calculators
Fire protection engineering depends on getting a handful of code-driven calculations exactly right, because the margin between a compliant design and a dangerous one is small. This category brings together the everyday fire-alarm and fire-fighting calculations used on real projects, each built directly from the governing standard — NFPA 72 for fire alarm and detection, NFPA 13 for sprinkler hydraulics, NFPA 20 for fire pumps, and NFPA 291 for hydrant fire-flow testing.
Fire alarm battery sizing follows NFPA 72: total capacity is the sum of standby current over the standby period plus alarm current over the alarm period, divided by a derating factor and multiplied by a 1.25 ageing margin. Sprinkler hydraulic demand under NFPA 13 combines design density with the most remote design area, with sprinkler flow given by Q = K√P. Fire pump selection under NFPA 20 must satisfy the 100% / 150% / churn points of the pump curve, and hydrant fire-flow under NFPA 291 scales the measured flow to a 20 psi residual. Every tool here shows the formula, a worked example, and exports a PDF report you can attach to a submittal.
Frequently Asked Questions
How do I size a fire alarm battery?
NFPA 72 battery capacity (Ah) = (Σ standby current × standby hours) + (Σ alarm current × alarm time in hours), then multiplied by a 1.25 ageing factor. A common requirement is 24 hours standby followed by 5 minutes in alarm. The Fire Alarm Battery calculator does this automatically.
What is the Q = K√P sprinkler formula?
For a sprinkler or nozzle, flow Q equals the discharge coefficient K multiplied by the square root of the pressure P. NFPA 13 hydraulic calculations combine this with a design density applied over the most hydraulically demanding area to find total system demand.
How is fire pump capacity defined in NFPA 20?
An NFPA 20 fire pump must deliver 100% of rated flow at rated pressure, at least 65% of rated pressure at 150% of rated flow, and no more than 140% of rated pressure at churn (zero flow). Sizing starts from the most demanding point of the protected system.
What does the hydrant colour code mean?
Per NFPA 291, hydrant bonnets and caps are colour-coded by available flow at 20 psi residual: light blue ≥1500 gpm, green 1000–1499 gpm, orange 500–999 gpm, and red below 500 gpm.