Diagonal Calculator
Rectangle Diagonal
—
Square Diagonal
—
How to Calculate Diagonals
The diagonal of a rectangle connects two non-adjacent corners and is calculated using the Pythagorean theorem: d = √(L² + W²). For a square, since L = W = s, this simplifies to d = s√2.
Diagonal measurements are useful in construction (checking if walls are square), interior design (fitting furniture), and screen sizing (TVs and monitors are measured diagonally).
A rectangle has two equal diagonals that bisect each other. A square also has two equal diagonals, but they bisect each other at right angles. This calculator computes diagonals for both shapes from the dimensions you provide.
Frequently Asked Questions
How do you calculate the diagonal of a rectangle?
Use the Pythagorean theorem: d = √(length² + width²). A 6×8 rectangle has diagonal = √(36+64) = √100 = 10.
What is the diagonal of a square?
d = side × √2 ≈ side × 1.4142. A square with side 10 has diagonal ≈ 14.14.
Are the diagonals of a rectangle equal?
Yes, both diagonals of a rectangle are equal in length. They bisect each other but do not cross at right angles (unlike in a square).
How is screen size measured?
Screen size (for TVs, monitors, phones) is measured along the diagonal. A 55-inch TV has a 55-inch diagonal measurement.