You can calculate only the upper excluded limit of value of area of a rectangle say A m2 when merely its diagonal length is known as say D m using the formula. It is an online Geometry tool requires two length sides of a rectangle. Now that you know how to find the area of a rectangle lets take a deep dive into the manual rectangle area calculation.
W 2 100.
A D2 2 This calculated value of the area of the triangle is the limiting value that can be approached but not reached. Simply plug the length and the diagonal into the formula above. This is the time to know how to calculate the area of a rectangle length of opposite sides perimeter etc. Using the Pythagorean theorem.