How to Find the Measure of the Diagonal of a Door

If you regularly move furniture or large objects through your home or are planning on getting some new furniture, you have to be sure that you can get it through your door. For large objects, the easiest method is to turn it diagonally and carry it through the door. For this to be effective, you must know the diagonal measurement of your doorway or the measurement from the base of the doorway to the opposite side at the top. You can use the Pythagorean theorem to measure the diagonal of the doorway as the hypotenuse of a right triangle.

Tape measure
Calculator

Instructions

- 1
  Place the end of the tape measure at the floor next to the doorway. The zero mark should be even with the inside of the door frame. Note the measurement from this point to the opposite side of the doorway. Assume you have a doorway 24 inches wide.
- 2
  Place the zero marking of the tape measure at the opposite corner just inside the top of the door frame opposite your previous measurement; if you measured from the left side of the floor you would measure from the top right corner. Assume your doorway is 78 inches tall.
- 3
  Take the square of each number: 576 and 6,084. Add these two numbers and you get 6,660. Find the square root of the total, which is 81.6. Your doorway's diagonal is therefore 81.6 inches.

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