Rectangle Calculator
Calculate rectangle area, perimeter and diagonal from positive length and width measurements.
What would you like to do next?
Turn two rectangular dimensions into three checks
Enter length and width to calculate area, perimeter and corner-to-corner diagonal. These outputs support flooring, framing, screen layout and classroom geometry while keeping the relationship between measurements visible. The diagonal uses the Pythagorean theorem, so it can also help check whether a measured rectangular space is approximately square at the corners.
Measure the shape that is actually present
The model assumes four right angles and opposite sides of equal length. Split L-shaped or irregular spaces into valid rectangles and add their areas rather than forcing one bounding box. Use one consistent unit for both dimensions, then apply waste, joints, borders or clearance as separate project decisions instead of hiding them inside the geometric result.
Frequently asked questions
How is the diagonal calculated?
It is the square root of length squared plus width squared.
Can length and width use different units?
No. Convert both measurements to one unit before calculating.
Does the result include material waste?
No. It provides geometric area only.