Math

Screen Diagonal Calculator

Calculate TV & Monitor Screen Diagonal

Measure the width and height of your screen's visible area, then enter them as Leg A and Leg B to calculate the diagonal. The standard 16:9 aspect ratio means width ≈ diagonal × 0.872 and height ≈ diagonal × 0.49.

Pythagorean Theorem Tips

Click to show tips

Try an Example

Pick a scenario to see how the calculator works, then adjust the values

Ladder Against Wall

A 10-foot ladder leans against a wall with the base 6 feet away. How high does it reach?

Key values: Leg a = 6 ft · Hypotenuse c = 10 ft · Solve for leg b

TV Screen Diagonal

Find the diagonal of a TV with a 16:9 aspect ratio (width 40", height 22.5").

Key values: Width = 40 in · Height = 22.5 in · Find diagonal

Classic 3-4-5 Triangle

Verify that sides 3, 4, and 5 form a right triangle (the most famous Pythagorean triple).

Key values: Sides: 3, 4, 5 · Right triangle · Primitive triple

Documentation

This calculator is also known as Screen Diagonal Calculator.

Read the complete guide

How Screen Sizes Work

TV and monitor sizes are measured diagonally. A "55-inch TV" means the diagonal from one corner to the opposite corner measures 55 inches. The actual width and height depend on the aspect ratio (usually 16:9).

Examples

Verifying a 55-inch TV

Measure the visible area: 48 in wide and 27 in tall.

Diagonal = √(48² + 27²) = √(2304 + 729) = √3033 ≈ 55.07 in.

Key takeaway: The diagonal matches the advertised 55-inch size.

Screen Shopping Tips

Make informed display purchases:

Measure the visible area, not the bezel
For 16:9 screens, width is approximately 87% of the diagonal
Consider viewing distance: a larger diagonal is not always better

Frequently Asked Questions about Screen Diagonal Calculator

How is a TV screen size measured?

TV and monitor sizes are measured diagonally from one corner to the opposite corner. A "55-inch TV" means the diagonal measures approximately 55 inches.

How do I verify my TV size?

Measure the visible width and height (excluding bezel), enter them as the two legs, and the calculator computes the diagonal. If it matches the advertised size, the specs are accurate.

What are the width and height of a 16:9 screen given the diagonal?

For a 16:9 screen, width is approximately 87.2% of the diagonal and height is approximately 49.0% of the diagonal. For example, a 55-inch TV is about 47.9 inches wide and 27.0 inches tall.