DOOR FIT / FREE TOOL
Door bottom gap checker
Record three clearance measurements along a closed door. Compare minimum, maximum and variation before selecting a sweep or contacting a manufacturer.
Example: why an average is misleading
With a 3/16-inch gap at one side, 1/4 inch in the middle and 5/16 inch at the other side, the smallest gap is 3/16 inch, the largest is 5/16 inch and the difference is 1/8 inch. Choosing by the average alone could lead to rubbing at one end or poor contact at the other.
Limitations and safe measurement
Readings are only as reliable as the reference surface and your ruler. Do not reach under a moving door or force a gauge into the sweep. For fire-rated, egress, security or commercial doors, use the assembly manufacturer's approved products and instructions.
Useful references
The U.S. Department of Energy door weatherstripping checklist emphasizes reducing air infiltration without impairing door operation.
What a three-point spread can tell you — and what it cannot
| Observation | Check before buying |
|---|---|
| Clearance increases steadily toward the latch side | Compare hinge and door alignment before using a deeper sweep. |
| Gap is small in the center but larger at both ends | Check threshold profile and whether the door-bottom seal is deformed. |
| Gaps look similar but a draft remains at one corner | Inspect the corner seal pad and jamb weatherstrip separately. |
| Door catches or the deadbolt no longer engages smoothly | Stop the adjustment. Restoring safe operation takes priority over closing a measured gap. |
A measurement record to keep
Record the gap readings, the unit chosen, a photo of the hinge/latch sides, the door's opening direction, the specific threshold surface measured and the make/model of any candidate seal. The threshold guide explains why an adjustable cap must be identified before touching a screw. Never turn the numeric spread into a required adjustment height: the calculator shows variation, not an allowed clearance or sweep recommendation.
The U.S. Department of Energy distinguishes weatherstripping for moving joints from caulk at stationary joints. For rated or security doors, the tested assembly instructions govern modifications.