Can I use decimals and change units without losing the data?

Yes. We accept dot or comma decimals and validate your input to avoid errors. When you switch units, we recalculate every conversion automatically.

How is the diagonal calculated and what does it represent?

We apply the Pythagorean theorem: d = √(base² + height²). The diagonal reflects the maximum span of the rectangle and is used, for example, to compare screens or panels.

Does the calculator store or send my data?

No. All computations happen in your browser and we don’t store any of the measurements you enter.

Rectangle area calculator

Q: How do you calculate the area of a rectangle?

Multiply the base by the height: A = base × height. Enter both lengths and click Calculate to instantly get area, perimeter, diagonal and aspect ratio.

Q: What is the perimeter shown for?

The perimeter indicates the total outline of the rectangle. It is helpful to know how much trim, skirting or edging you need around the surface.

Compute area, perimeter, diagonal and aspect ratio from side lengths. Includes unit conversions and decimal control.

Rectangle area

Compute area, perimeter, diagonal, and aspect ratio from two sides.

A = width × height

Input data

Width e.g. 4.25

Comma or dot decimals accepted.

Height e.g. 3

Values must be ≥ 0.

Units

The main area is shown in the chosen unit².

How it works

Enter width and height using the same unit.
Click Calculate to get the area and extra metrics.
Switch the unit selector to convert the outputs instantly.

Diagonal uses Pythagoras: √(width² + height²).

Results

Main area

Enter the values and press Calculate

Width and height in the selected unit

Geometric visualization

The rectangle is drawn at a relative scale with width, height and diagonal.

Calculate to see the rectangle.

Perimeter

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Diagonal

—

Aspect ratio

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Area conversions

mm²

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cm²

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m²

—

in²

—

ft²

—

Includes all conversions.

Formulas used

Area: A = width × height.
Perimeter: P = 2 × (width + height).
Diagonal: d = √(width² + height²).
Aspect ratio: width : height simplified.

Typical uses

Measure rooms, screens, boards, or fabric pieces.
Plan rectangular gardens or floor layouts.
Switch between metric and imperial units in one click.

How do you calculate the area of a rectangle?

Multiply width by height: A = width × height. Enter both sides and hit Calculate to instantly get area, perimeter, diagonal, and aspect ratio.

Can I use decimals and switch units without losing my data?

Yes. Dot or comma decimals are accepted and validated. When you change the unit, we recalc the main result and all conversions automatically.

What is the perimeter shown for?

The perimeter is the total outline of the rectangle. It helps you estimate trim, skirting, framing, or any border material.

How is the diagonal computed and what does it tell me?

We apply the Pythagorean theorem: d = √(width² + height²). The diagonal is the longest distance across the rectangle and is handy for comparing screens or panels.

Do you store or send the values I type?

No. Everything is calculated locally in your browser; none of your measurements are saved or transmitted.

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