GlenCalc

Diagonal calculator

A rectangle is square when both diagonals are equal. The diagonal should equal √(length² + width²).

Your answer

Diagonal23.324 ft
In feet and inches23 ft 3.89 in
3-4-5 checkMark 9 ft and 12 ft from a corner; they should be 15 ft apart

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How we worked it out

Updated as you change the numbers.

  1. Diagonal = √(length² + width²) (Pythagoras).

Method and assumptions

Builders square a layout by adjusting it until both diagonals measure the same. The 3-4-5 triangle (and its multiples like 6-8-10) gives a right angle without a calculator.

Questions

What is the diagonal of a 20 × 12 ft deck?

23.324 ft: 23 ft 3 7/8 in.

Sources

Method and figures checked on . Every worked answer on this page is covered by an automated test. Found a mistake? Tell us.

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