Fire / Hp-A Calculator

Calculates the fire section factor (Hp/A) for a symmetric I/H section — the figure your fire protection supplier needs to select a coating or board thickness from their own certified product data.

Exposure condition:
Protection method:
Standards used on this page:
  • BS EN 1993-1-2:2005+A1:2014 (Eurocode 3, Part 1-2: Structural fire design) — defines the Hp/A (Am/V) section factor
Accuracy & scope note:
  • This tool calculates Hp/A only — it does not calculate a required fire protection thickness. That depends on the specific protection product's own tested thermal properties, which come from manufacturer fire testing and certification, not a Eurocode formula.
  • "Contour" method assumes protection follows the actual steel profile (sprays, intumescent paint). "Box" method assumes a simple rectangular envelope (board protection) — this always gives a lower, less conservative Hp/A than the true contour value.
  • Assumes a symmetric I/H section with sharp (unfilleted) corners, consistent with the other modules on this site.
  • "3-sided" exposure assumes the top flange is in full, continuous contact with a concrete slab along its whole width. If there's any gap, use 4-sided exposure instead.
This tool provides preliminary, indicative structural calculations only, intended to assist with initial sizing and understanding. It is not a substitute for assessment by a qualified structural engineer or fire engineer, and cad-steel.co.uk accepts no responsibility for its use in any final design. Always have fire protection specifications checked and confirmed against manufacturer's certified test data before construction.