For Engineers
Engineer Tools
Quick calculators and reference tables for fire & security work on site — battery sizing, extinguisher provision, detector spacing and the standard category tables, all in one place.
These tools give an indicative figure fast, using the standard methodology from BS 5839‑1, BS 5306‑8 and related guidance. They're a starting point for site work, not a substitute for professional judgement or the current edition of the relevant standard — always confirm final figures against the standard and the equipment manufacturer's instructions.
Available Tools
Battery Standby Calculator
Work out required standby battery capacity (Ah) from standby and alarm current readings, for 24hr or 72hr standby periods per BS 5839‑1.
Battery Standby Calculator →Fire Extinguisher Calculator
Minimum fire rating and extinguisher count from floor area, per BS 5306‑8 — including the 26A/storey minimum and 2‑per‑floor rule.
Fire Extinguisher Calculator →False Alarm Rate Calculator
Track false alarms against total activations to flag systems drifting outside an acceptable rate.
False Alarm Rate Calculator →Detector Spacing Calculator
Maximum smoke/heat detector spacing for corridors of a given width per BS 5839‑1.
Detector Spacing Calculator →BS 5839‑1 Category Table
Quick reference for M, L1–L5 and P1–P2 categories and what each covers.
BS 5839‑1 Category Table →BS 5839‑6 Category Table
Grades and LD1–LD3 categories for domestic fire detection, current post‑2019‑revision.
BS 5839‑6 Category Table →Intruder Alarm Grades
Grades 1–4 per PD 6662 / EN 50131 and what risk level each is intended for.
Intruder Alarm Grades →Need something added?
If there's a calculation or reference table that'd help on site, let us know and we'll look at adding it.