How to calculate the diagonal of a rectangle?

The diagonal is calculated using the Pythagorean theorem: d = sqrt(width² + height²). For example, a 36-inch by 48-inch rectangle has a diagonal of 60 inches.

What is the 3-4-5 rule in carpentry and squaring?

The 3-4-5 rule states that if one side of a corner measures 3 feet, the perpendicular side measures 4 feet, and the diagonal between them measures exactly 5 feet, the corner is a perfect 90-degree right angle.

How are TV screen sizes measured?

Television and computer monitor sizes (e.g. 55-inch or 65-inch) are measured diagonally from the top-left corner to the bottom-right corner of the viewable display panel.

Geometry & Carpentry

Diagonal Calculator (US)

Quickly calculate the diagonal of rectangles, TV screens, square layouts, right triangles (Pythagorean 3-4-5), and 3D boxes in inches, feet, and yards.

Diagonal Length -

Measurement Unit

Width / Length (a) 48 in

Height / Depth (b) 27 in

Depth / Height (c) 18 in

Calculated Diagonal Length (d)

Formula: d = √(a² + b²)

Diagonal (d)

Surface Area

Perimeter

Diagonal Angle (θ)

Standard Dimensional & Unit Conversions

Unit	Diagonal Length	Side A (Width)	Side B (Height)	Area