Rectangle Area Calculator
Compute rectangle area, perimeter, diagonal, aspect ratio, and an optional material cost. Start from length–width, perimeter–side, or diagonal–side.
L & W in this unit
P = 2(L + W)
other side is derived
must be < diagonal
Rectangle formulas used
Area: \( A = L \times W \)
Perimeter: \( P = 2(L + W) \)
Diagonal: \( d = \sqrt{L^2 + W^2} \)
From perimeter + one side: \( W = \frac{P}{2} - L \)
From diagonal + one side: \( W = \sqrt{d^2 - L^2} \)
FAQs
Can I use different units for length and width?
No — convert to a single unit first (e.g. all in inches) so the area can be computed correctly.
What if length equals width?
Then your rectangle is a square. The calculator will notice and tell you.
What does cost per unit² mean?
If you know, for example, that flooring costs 20 €/m², enter 20 and we’ll multiply area × 20.