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Results
Enter your dimensions above and the results appear here.
About the Rectangle Calculator
The rectangle calculator is a free online tool: area, perimeter, diagonal and circumradius. Enter length (l) and width (w) and the results update instantly, alongside a labelled diagram so you always know which measurement goes where.
Choose your input unit (mm, cm, m, km, in, ft or yd) and optionally show the results in a different one: lengths, areas and volumes are converted correctly. Every answer shows the formula behind it, and the calculation runs in your browser, so nothing is uploaded.
Rectangle Calculator example
Length (l) = 8 cm
Width (w) = 5 cmArea = 40 cm²
Perimeter = 26 cm
Diagonal = 9.434 cm
Circumscribed circle radius = 4.717 cm
Aspect ratio = 1.6How to use the Rectangle Calculator
- Pick the unit your measurements use. All dimensions must share the same unit.
- Enter length (l) and width (w). Focus a field to highlight the matching label on the diagram.
- Read the results as you type. The largest card is the main answer; the others are the related measurements.
- Copy a single value, copy everything, or share a link that keeps your inputs.
Rectangle Calculator FAQ
What formulas does the rectangle calculator use?
A = l × w; P = 2(l + w); d = √(l² + w²).
Can I use different units?
Yes. Pick the input unit and, if you like, a different output unit. Area results are shown in squared units and volumes in cubed units.
Is this rectangle calculator free and private?
Yes. It is free with no sign-up, and calculations happen on your device, so your numbers are never sent to a server.
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