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Geometry Calculator Online

Diagonal Calculator Online for Rectangle, Square, Box, TV Screen, and Room

This diagonal calculator helps you find diagonal length quickly using the correct diagonal formula for each shape. Use it as a diagonal of rectangle calculator, diagonal of square calculator, diagonal of cuboid calculator, screen diagonal calculator online, and room diagonal calculator online.

Primary Result - Enter values to calculate.

Diagonal of Rectangle Calculator

Find diagonal of rectangle given two sides.

Diagonal Length-
Perimeter-
Area-
Formulad = sqrt(l² + w²)

Diagonal of Square Calculator

Square diagonal length formula with instant output.

Diagonal-
Perimeter-
Area-
Formulad = s × sqrt(2)

Diagonal of Cuboid Calculator

3d diagonal of box calculator online.

Space Diagonal-
Face Diagonal (L-W)-
Face Diagonal (L-H)-
Face Diagonal (W-H)-

Number of Diagonals in Polygon Calculator

Formula for pentagon, hexagon, and n-sided polygons.

Total Diagonals-
From One Vertex-
Formulan × (n - 3) ÷ 2

Screen Diagonal Calculator Online

TV diagonal calculator online with resolution and optional PPI.

Diagonal (px)-
Aspect Ratio-
Diagonal (in)-
Diagonal (cm)-

Room Diagonal Calculator Online

Diagonal distance of room corner to corner and squareness check.

Expected Diagonal-
Difference-
StatusAdd measured value
Live representative diagram updates based on selected mode and inputs.

Diagonal Formula Guide for Students, DIY Users, and Screen Buyers

This page combines a pythagorean theorem calculator style workflow with practical tools. It supports diagonal measurement calculator online use cases for homework, woodworking, construction measurement, and TV size comparison.

How to Find Diagonal of Rectangle Online

Use this rectangle diagonal length calculator when you know length and width.

d = sqrt(length² + width²)

Diagonal of Cube and Cuboid

For a cuboid, the space diagonal comes from all three dimensions.

d = sqrt(l² + w² + h²)

Polygon Diagonals Formula

Quickly answer exam-style questions such as how many diagonals does a hexagon have.

n × (n - 3) ÷ 2

Screen and TV Diagonal Measurement

Use resolution and PPI to estimate diagonal in inches, useful for monitor and TV size checks.

FAQ

What is diagonal of a rectangle?

It is the straight distance from one corner to the opposite corner.

What is diagonal of square formula?

Diagonal equals side multiplied by square root of 2.

How to measure TV screen diagonal?

Measure only the visible display area corner-to-corner, not bezel.

How to square a room using diagonal?

Compare expected diagonal from length and width with measured corner-to-corner distance.