Rectangle Area Calculator
Find the area of a rectangle from its width and length — fast, using S = a · b.
Formula
S = a · b
a is the width of the rectangle, b is its length.
About the rectangle area calculator
The area of a rectangle is the size of the region enclosed by its four sides. It equals the product of two adjacent sides: the width and the length.
For a correct result, enter both sides in the same unit of measurement. A square uses the same formula — its width and length are simply equal.
Every calculation runs instantly right in your browser — nothing is uploaded, so your numbers stay completely private.
Benefits
Instant results
The area updates immediately as you type the width and length.
Simple formula
Uses the exact formula S = a · b with no hidden rounding.
Fully private
All math happens locally in your browser with no uploads.
Frequently asked questions
How do I find the area of a rectangle?
Multiply the width by the length: S = a · b. The calculator does this automatically.
How is area different from perimeter?
Area is the size of the region inside (in square units), while perimeter is the total length of all sides (in linear units).
Can I use this for a square?
Yes, a square is a special rectangle. Enter equal width and length to get the area of a square.
What unit will the area be in?
If the sides are in centimeters, the area is in square centimeters (cm²). Both sides must use the same unit.
Can I enter decimal values?
Yes, you can enter decimals such as 3.5. The calculator handles fractional sides correctly.