How do you calculate clear opening width of a fire door?
The clear opening width refers to the unobstructed horizontal space through which a person can pass when the door is open. This measurement is typically taken when the door is opened to a 90-degree angle. For single doors, it’s measured from the face of the door leaf to the opposite door frame or jamb. Or for double doors, the measurement is taken between the two door leaf faces.
How to Measure Clear Opening Width?
Firstly, Open the Door to 90 Degrees: Ensure the door is fully opened to a 90-degree angle. Next, Measure from the Door Face to the Frame: For single doors, measure from the face of the door leaf to the opposite door frame or jamb. For double doors, measure the gap between the two door leaf faces. Lastly, Account for Projections: Be aware of any hardware that might reduce the clear width, such as door handles or panic bars. These should be subtracted from the measurement if they protrude into the opening.
It’s not as complicated as you may think – below is a quick calculation you can use along with a drawing.
The formula is as below:
Single Doors = Door Width + 6mm – Doorstop Thickness – Door Thickness
Double Doors = Door Width 1 + Door Width 2 + 9mm – (Door Thickness x2)
Read our post on Understanding Fire Door Sizing Requirements to learn more on compliant openings and egress paths.
