The Rectangle Calculator finds area, perimeter and diagonal from length and width, with a square mode when all four sides are equal. Enter any two independent measures when the engine supports them and read the rest with a labelled diagram of the figure.
Rectangles appear on floor plans, screens and boxes before they become prisms. The diagonal uses the Pythagorean theorem on length and width, which is why the same 3-4-5 triangle logic appears here and on right-triangle pages.
Calculate a rectangle from length and width
A rectangle has four right angles and opposite sides equal in pairs. Length and width are the two distinct edge lengths, and together they fix area, perimeter and diagonal. Enter the known pair in the matching fields and leave derived values blank unless checking a given answer from a textbook.
The diagram labels length and width on adjacent sides and draws the diagonal as a dashed segment. Units stay consistent: if length and width are in meters, area is square meters. Square mode collapses the two fields when all sides must match.
Calculate the area of a rectangle
Area counts unit squares that cover the interior, which for a rectangle is the product of the two adjacent side lengths. Unlike a triangle, no extra height line is needed because the sides already meet at right angles. Square mode uses the same formula with length equal to width.
A = length * widthFor length 4 and width 6:
A = 4 * 6 = 24Calculate the perimeter and diagonal
Perimeter is the distance once around the figure, walking all four edges. Diagonal is the straight segment joining opposite corners and equals the hypotenuse of a right triangle with legs length and width. Both formulas are linear or Pythagorean combinations of the same two inputs.
P = 2 * length + 2 * width
diagonal = sqrt(length^2 + width^2)For 4 by 6:
P = 2 * 4 + 2 * 6 = 20
diagonal = sqrt(4^2 + 6^2) = sqrt(16 + 36) = sqrt(52) approx 7.21Calculate a square
A square is a rectangle with all sides equal, so one side length determines every measure. Square mode sets length equal to width automatically and labels the figure as a square on the diagram. Perimeter is four times the side, and area is the side squared.
A = s^2
P = 4 * s
diagonal = s * sqrt(2)When s = 6, area is 36, perimeter is 24 and diagonal is 6 * sqrt(2) approx 8.49. The 4 by 6 rectangle case above remains the non-square reference fixture.
Solve a rectangle 4 by 6
Use length 4 and width 6 as the standard worked rectangle. Area and perimeter are integers. The diagonal leaves a surd under the square root unless rounded for display. 1. Area
A = 4 * 6 = 242. Perimeter
P = 203. Diagonal
d = sqrt(52) approx 7.21Frequently asked questions
How do I find the area of a rectangle?
Multiply length by width. For 4 by 6 the area is 24 square units.
How do I find the perimeter?
Add all sides or use P = 2 * length + 2 * width. For 4 by 6 the perimeter is 20.
How is the diagonal found?
Apply the Pythagorean theorem: diagonal = sqrt(length^2 + width^2). For 4 and 6, sqrt(52) approx 7.21.
What is square mode?
Square mode sets length equal to width so one side input defines a square.
Can a rectangle and square share the same page?
Yes. Square mode is the special case where length equals width.
What units does area use?
Square units of the side length, such as ft^2 when sides are in feet.
Is the diagonal the same as a space diagonal?
No. This diagonal lies in the plane of the rectangle. A box space diagonal uses a third dimension on the rectangular prism page.
Summary
Rectangle Calculator returns the measures named in the sections above, with substituted arithmetic for every formula and a labelled figure drawn to the entered dimensions. Worked numbers on this page match the geometry reference fixtures.