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Math

Rectangle Calculator

Find a rectangle’s area, perimeter and diagonal from length and width.

Exact method explained belowEditable inputs
Geometry desk
Geometry desk

Match each dimension to the shape and keep units consistent.

See the method

Set the dimensions

Runs on your device

Your measurement

Your result

Let’s calculate.

Use the Calculate button to see your result.

Review the method below for assumptions and conventions.

How to use this tool

  1. Enter length, width.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

Input reference and sample values

Use the units and choices shown for each field. Sample values are provided for practice, not as recommendations.

InputFormat and unitsSample
LengthNumeric value. Zero or positive.8
WidthNumeric value. Zero or positive.6

Result for these sample inputs

48 square units
Perimeter
28
Diagonal
10

Select Try the example in the form to load these values and calculate them again. This replaces the current form inputs. Compare the result with the method and worked explanation below.

The method, explained

Area = length × width. Perimeter = 2(length + width). Diagonal = √(length² + width²).

A WORKED EXAMPLE

An 8 by 6 rectangle has area 48, perimeter 28 and diagonal 10.

What to keep in mind

Both dimensions use the same length unit. The formula assumes four right angles; it does not describe an arbitrary quadrilateral.

Common questions

What units are used for area?

The length unit squared. Meter inputs produce square meters.

Can this calculate a square?

Yes. Use equal length and width.

Methodology maintained by ClarityKit. How these tools are built and checked.