Measure Wall to Wall Accurately by Marking 10 Inches and Adding It Back

The Problem

An inside measurement — wall to wall, jamb to jamb, inside a cabinet opening — is the one a tape measure is worst at. Hook the tape in one corner and the last few inches bend up the far wall, so the blade curves away from the surface you're trying to reach and the number you want is on the part that's bent. Most people push the tape into the corner, eyeball the bend, and round.

That guess goes straight into a piece of trim or a shelf. A quarter inch long and the piece won't drop in; a quarter inch short and you're looking at the gap for as long as you own the room.

The Technique

Take the corner out of the measurement entirely by putting your reference point somewhere flat.

1. Hook your tape on one wall and mark the wall — or the floor — at exactly 10 inches.
2. Move to the opposite wall. Hook the tape there and read across to your mark.
3. Add 10 inches to what you read. That's the span.

If the second reading is 43-1/4, the wall-to-wall dimension is 53-1/4. Nothing was bent, nothing was estimated, and both numbers were read off a flat run of tape with the blade lying against the surface.

Ten is arbitrary — it's just an easy number to add in your head under a cabinet. Any round number works as long as you use the same one at both ends of the arithmetic.