CalcLibrary

Rectangle Calculator

Solve a rectangle from the measurements you already have. Start with length and width for the full geometry, or switch to area, perimeter, or diagonal modes to reverse-solve the missing side.

Active rectangle equation
m
m
Examples

Use the default length-and-width path to get area, perimeter, and diagonal in one pass.

Area
24 m²
Perimeter
22 m
Diagonal
8.54 m
Formula recap
\text{area} = \text{length} \cdot \text{width} = 8 \cdot 3 = 24, P = 2(l + w) = 2(8 + 3) = 22, d = \sqrt{l^{2} + w^{2}} = \sqrt{8^{2} + 3^{2}} = 8.544004

Both sides were known, so the calculator applied the direct rectangle formulas.

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Examples

How It Works

Formula

area=length⋅width\text{area} = \text{length} \cdot \text{width}

perimeter=2(length+width)\text{perimeter} = 2(\text{length} + \text{width})

diagonal=length2+width2\text{diagonal} = \sqrt{\text{length}^{2} + \text{width}^{2}}

Variables

length\text{length}

One side of the rectangle(selected unit)

width\text{width}

The perpendicular side of the rectangle(selected unit)

area\text{area}

Surface inside the rectangle(selected unit²)

perimeter\text{perimeter}

Distance around the rectangle(selected unit)

diagonal\text{diagonal}

Corner-to-corner distance(selected unit)

Pick the measurement pair you know, enter the two values, and the calculator reconstructs the rectangle. If you entered both sides, area, perimeter, and diagonal are direct formulas. If you entered area, perimeter, or diagonal with one side, the calculator first solves the missing side, then derives the remaining geometry.

Frequently Asked Questions

01What formulas does this rectangle calculator use?
It uses the three core rectangle relationships: area = length × width, perimeter = 2 × (length + width), and diagonal = √(length² + width²). Reverse-solve modes simply rearrange those same relationships.
02Can it solve a missing side from area and one known side?
Yes. If you know the area and one side, divide area by that side to recover the missing dimension. The calculator then fills in perimeter and diagonal from the solved rectangle.
03Why would diagonal plus a side ever be invalid?
Because the diagonal is the longest line in a rectangle. If the diagonal is shorter than or equal to the side you entered, no real rectangle can match those measurements.
04Does it also work for squares?
Yes. A square is just a rectangle with equal length and width. When both sides match, the calculator keeps the same formulas and simply makes the square case visible in the result note.
05What unit does the area use?
Area is shown in the squared form of the length unit you selected: m² for meters, cm² for centimeters, ft² for feet, and in² for inches.

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