Rectangle calculator — area and perimeter
Enter the two sides of a rectangle and the calculator gives the area and the perimeter at once. For a square, enter the same value twice.
A rectangle with sides 8 and 5 has an area of 40.00 and a perimeter of 26.00.
Formula
a and b are the side lengths. Area is the product of the sides; perimeter is twice their sum.
How we got there
Area is in square units and perimeter in ordinary ones — two different quantities from the same two numbers.
How to work out the area and perimeter by hand
- Multiply the sides for the area
8 × 5 = 40 square units.
- Add the sides and double for the perimeter
(8 + 5) × 2 = 26 units.
- For a square, enter the same side twice
A square is a rectangle with equal sides, so the formulas are unchanged.
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Frequently asked questions
Multiply its sides. For sides of 8 and 5 the area is 40.
Add both sides and multiply the total by two: (8 + 5) × 2 = 26.
Enter the same side in both fields — the area of a square is the side squared.
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