How to use this rectangle calculator
Enter the requested values above and select Calculate. The result updates immediately on the page, so you can change one value and compare different scenarios without leaving the calculator.
Formula and method
Example
A 12 by 8 rectangle has area 96 and perimeter 40.
What this calculator is useful for
Calculate area, perimeter and diagonal of a rectangle from length and width. It is designed for quick estimates and everyday problem solving. When a calculation affects a contract, tax filing, medical decision or other high-stakes situation, verify the result with the appropriate professional or authoritative source.
Frequently asked questions
What does the Rectangle Calculator calculate?
Calculate area, perimeter and diagonal of a rectangle from length and width.
How does the calculation work?
Area = length × width. Perimeter = 2(length + width). Diagonal = √(length² + width²).
Is this calculator free?
Yes. ERICH Calculators is free to use and no account is required.