Measure an Inside Span by Adding Two Overlapping Tape Readings

The Problem

An inside span — wall to wall, jamb to jamb — defeats a tape measure read straight: the hook sits in one corner, the case crowds the other, and the last few inches bend up the far side where you can't read them. Guessing at the bend is how trim comes up short.

The Technique

1. Hook or butt the tape in one corner and mark a round, easy-to-add number partway across the span — 30" in the creator's demo.
2. Pull the tape from the opposite side to that same mark and read it — here, 25-3/4".
3. Add the two: 30 + 25-3/4 = 55-3/4". That's the exact inside span.

Picking a round number for the first mark is the whole trick — the addition happens in your head with no fraction-on-fraction arithmetic.