CDConvertibleData
Geometry calculator

Rectangle Calculator

Calculate rectangle area, perimeter and diagonal from length and width.

✓ Tested formula✓ Instant result✓ Private by design
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Enter your valuesResults update instantly as you type.

✓ Your numbers stay on this device.

Understand the answer

Formula and method

FormulaArea = length × width; perimeter = 2(length + width); diagonal = √(length² + width²).

The diagonal follows the Pythagorean theorem because adjacent rectangle sides meet at a right angle.

Worked example

A 10 by 6 rectangle has area 60, perimeter 32 and diagonal about 11.6619.

How to use this calculator

  1. Enter the values using the labels and units shown.
  2. Review the live result and supporting details.
  3. Check the formula, example and assumptions before using the answer.

Assumptions and limits

  • Length and width use the same unit.

Reference

Formula reviewed 2026-07-15

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