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Math & Numbers Runs in browser Updated 30 Mar 2026

Area & Perimeter Calculator

Calculate area and perimeter for rectangles, triangles, circles, trapezoids, ellipses, and regular polygons with formula diagrams.

l = ?w = ?

Rectangle Dimensions

Results

Area

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Perimeter

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Enter the required dimensions above to see results.

All Formulae

Rectangle A = l×w, P = 2(l+w)

Square A = s², P = 4s

Triangle A = bh/2, P = a+b+c

Parallelogram A = bh, P = 2(b+s)

Trapezoid A = (a+b)h/2, P = a+b+leg&sub1;+leg&sub2;

Rhombus A = d&sub1;×d&sub2;/2, P = 4×√((d&sub1;/2)²+(d&sub2;/2)²)

Ellipse A = πab, P ≈ π(3(a+b) − √((3a+b)(a+3b)))

Regular Polygon A = ns²/(4tan(π/n)), P = ns
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How to use Area & Perimeter Calculator

  1. Select a shape

    Choose from rectangle, square, triangle, parallelogram, trapezoid, rhombus, ellipse, or regular polygon using the shape selector.

  2. Enter dimensions

    Fill in the required measurements. The input labels update to match your shape — base, height, radius, side length, etc.

  3. Read area and perimeter

    Results appear instantly with the formula used. Both area and perimeter are displayed with appropriate units.

  4. Check the diagram

    The labeled SVG diagram confirms which dimension corresponds to each input field.

  5. Adjust and compare

    Change any dimension to instantly see how it affects area and perimeter — useful for optimization problems.

Area & Perimeter Calculator FAQ

What shapes are supported?
Rectangle, square, triangle, parallelogram, trapezoid, rhombus, ellipse, and regular polygons with 3-12 sides. For circles, use the dedicated Circle Calculator.

What formula is used for triangle area?
Area = ½ × base × height. If you know all three sides instead, use Heron's formula: s = (a+b+c)/2, Area = √(s(s-a)(s-b)(s-c)).

What formula is used for a trapezoid?
Area = ½ × (a + b) × h, where a and b are the parallel sides and h is the height. Perimeter = a + b + c + d for all four sides.

How do I calculate the area of a regular polygon?
Area = (n × s² × cot(π/n)) / 4, where n is the number of sides and s is the side length. The calculator handles this automatically.

What is the difference between area and perimeter?
Area measures the space inside a 2D shape (square units). Perimeter measures the total length of its boundary (linear units).

Can I use this for homework?
Yes. The formula for each shape is displayed alongside the result so you can verify your work and understand the method.

What units should I use?
Any consistent unit. If you enter dimensions in meters, the area is in square meters and the perimeter in meters.

What is a regular polygon?
A polygon where all sides and interior angles are equal. Enter the number of sides and side length to calculate its area and perimeter.

How is ellipse area different from circle area?
Circle area = π × r². Ellipse area = π × a × b, where a is the semi-major axis and b is the semi-minor axis.

Is any data sent to a server?
No. All calculations run entirely in your browser. Nothing is uploaded or stored.

Background

Select a 2D shape and enter its dimensions to instantly calculate area and perimeter with the correct formula shown. Supports rectangle, square, triangle, parallelogram, trapezoid, rhombus, ellipse, and regular polygons with 3 to 12 sides. Each result includes a labeled SVG diagram so you can confirm the dimensions match your problem. Ideal for homework, architecture, landscaping, and engineering sketches. Works for students from middle school through college and professionals who need fast geometry checks. The formulas shown include derivations so you can follow the math, not just copy the answer. Trapezoid area uses (a + b)/2 × h; ellipse uses π × a × b; polygon uses the standard apothem formula. No account, no ads in the tool area, and all processing stays in your browser — nothing is sent to a server. Results update instantly as you type, making it easy to explore how changing one dimension affects the others.

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