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Rectangle Calculator

Computes the area, perimeter and diagonal of a rectangle from its length and width. Lengths are unit-agnostic; the area is in the square of the input unit.

When to use

You need the area, perimeter or diagonal of a rectangle or square (enter equal length and width).

Do not use when: The shape is a box with depth (use rectangular-prism) or a slanted quadrilateral (use parallelogram or trapezoid).

Formula

area = length × width; perimeter = 2 × (length + width); diagonal = √(length² + width²); diagonal_angle_deg = atan(width / length)

Inputs

Parameter	Type	Unit	Required	Description
`length`	number	units	yes	Length of the rectangle. Range: > 0
`width`	number	units	yes	Width of the rectangle. Range: > 0

Outputs

Output	Type	Unit	Description
`area`	number	units²	length × width.
`perimeter`	number	units	2 × (length + width).
`diagonal`	number	units	√(length² + width²).
`diagonal_angle_deg`	number	degrees	Angle between the diagonal and the length side = atan(width / length).

Example

5 by 3: {"length":5,"width":3} → {"area":15,"perimeter":16,"diagonal":5.831,"diagonal_angle_deg":30.9638}

12 by 5: {"length":12,"width":5} → {"area":60,"perimeter":34,"diagonal":13,"diagonal_angle_deg":22.6199}

GET https://tttkmbb.com/api/v1/calculate/rectangle?length=5&width=3

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/rectangle (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/rectangle · Markdown: https://tttkmbb.com/geometry/rectangle.md · JSON definition: https://tttkmbb.com/geometry/rectangle.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="rectangle"
OpenAPI operationId: calculate_rectangle_properties
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

Wikipedia – Rectangle (reference)
Wolfram MathWorld – Rectangle (reference)

FAQ

Does it matter which side is the length?

No for area, perimeter and diagonal. Only diagonal_angle_deg is measured from the side entered as length.

How do I use it for a square?

Enter the same value for length and width; the diagonal is then side × √2 and the diagonal angle is 45°.

Related calculators

Rectangular Prism Calculator — Add a height to get a box's volume and surface area.
Parallelogram Calculator — Quadrilateral with slanted sides.
Flooring Calculator — Estimate flooring material for a rectangular room.