Rectangle calculator

Rectangle area = length × width. Perimeter = 2 × (length + width). Diagonal = √(length² + width²).

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Length

Width

Answer

…

Rectangle area = length × width. Perimeter = 2 × (length + width). Diagonal = √(length² + width²).

More results

Precision and calculation record

Decimal places in numeric results and text downloads

Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Step-by-step calculation

Inputs are substituted below. Each line evaluates the next operation; intermediate values are displayed to 12 significant digits while the calculation uses full precision.

Saved scenario

Save the current answer, then change an input to compare. This clears when you leave.

Formula and assumptions

Both dimensions must use the same length unit. The sides meet at right angles; this does not apply to a skewed quadrilateral.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-26

Using Rectangle calculator

Rectangle area = length × width. Perimeter = 2 × (length + width). Diagonal = √(length² + width²).

Both dimensions must use the same length unit. The sides meet at right angles; this does not apply to a skewed quadrilateral.

Next: Polygon calculator

A worked example

With length = 8, width = 3, the area is 24.

Next: Triangle calculator

Before you use the result

Both dimensions must use the same length unit. The sides meet at right angles; this does not apply to a skewed quadrilateral.

Example results for length

These examples use Width: 3. They are reference calculations, not recommended settings.

Length	Area
4	12
8	24
16	48

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