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Find rectangle area, perimeter, and diagonal.
▭ Area = width × height. Diagonal uses the Pythagorean theorem.
This calculator finds the area, perimeter, and diagonal of a rectangle from its width and height. One of the most practical calculations in daily life.
In the US, area is often measured in square feet. For a 12 × 15 foot room: 12 × 15 = 180 sq ft. To convert to square meters, multiply by 0.0929 (180 sq ft ≈ 16.7 m²).
The Rectangle Calculator lets you figure out rectangle calculatorinstantly, without reaching for a spreadsheet or doing the math by hand. Whether you're planning a budget, checking a loan, or working through homework, the tool applies the correct formula behind the scenes and shows the result the moment you enter your numbers.
Unlike a static chart or table, this calculator adapts to your exact inputs. You can adjust any value and see the outcome update in real time, which makes it easy to compare scenarios — for example, "what if the rate were 1% lower?" or "what if I paid an extra $50 a month?"
Common uses: people reach for this tool when they need to find a rectangle area from length and width, rectangle perimeter and diagonal, rectangle diagonal calculator, or square footage from sides.
Browser-based tools like this one have a few real advantages over installed software or manual methods:
The Rectangle Calculator is based on the following formula:
A = w × h
Variables: A = Area (square units) w = Width (units) h = Height (units)
Rectangle area. w = width, h = height.
Worked example: Step 1: w = 4.5 m, h = 3 m. Step 2: A = 4.5 × 3 = 13.5. Result: the rectangle's area is 13.5 m².
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