Fire / Hp-A Calculator

Calculate the section factor Hp/A (heated perimeter divided by cross-sectional area) for a symmetric I/H (W-shape), the geometric ratio a fire-protection supplier uses to select coating or board thickness. A higher Hp/A heats faster and needs more protection.

Standards context:Section factor Hp/A (units m-1), referenced to NBCC 2020 Division B fire-resistance provisions and CAN/ULC-S101 test methodology. Hp/A itself is a purely geometric ratio.
Note: Profile follows the section outline (spray / intumescent coatings);box is the smallest enclosing rectangle (board systems). 3-sided shields the top flange (e.g. a floor slab bearing on it). Area is from the idealised (sharp-corner) section, so Hp/A runs about 1% high versus the CISC filleted value - adequate for preliminary protection sizing.
Section
Exposure
This calculator 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 or fire engineer, and ca.cad-steel.com accepts no responsibility for its use in any final design.