Fire Door Gap Measurer

Measure the gap with a feeler or gap gauge, pick the gap type, and get an instant in-band / out-of-band verdict — with typical next steps when the gap is out of band.

Bands are self-written summaries of common fire-door installation practice (NFPA 80 conventions — check the current edition for exact sections). Your AHJ and the door manufacturer's listings take precedence.

Gap type

Measured gap (inches — decimal or fraction)

How to measure

With a feeler or gap gauge, measure top, middle, and bottom on both the hinge side and latch side; record the largest value with the door fully closed.

Verdict

Enter a measurement to get a verdict. Bands shown are common-practice conventions, not a substitute for the applicable standard or your AHJ's requirements.

About this band

Common band for door edge to frame: 1/16" – 3/16"

Commonly about 1/8", with ±1/16" tolerance (a 1/16"–3/16" band); based on common fire-door installation practice (NFPA 80 convention — check the current edition for the exact section). Too tight binds the door; too wide leaves a fire/smoke path.