How to Calculate the Area of Any Common Shape

To find an area you multiply or combine a shape's key measurements using its formula — length × width for a rectangle, ½ × base × height for a triangle, π × r² for a circle — and the right formula depends entirely on the shape. Rather than remember them all, you can let a tool pick the formula and do the arithmetic. The Area Calculator covers the five most common shapes, shows the exact formula it used, and returns the result directly in your chosen unit.

A practical helper for real projects

Area math turns up in DIY and construction more than anywhere else — flooring, painting, laying turf, tiling a wall — where getting the square footage right decides how much material to buy. Students also need it for geometry homework and quick checks. Because you choose the measurement unit up front (metres, centimetres, feet, inches or yards), the answer comes out in m², cm², ft², in² or yd² without any manual conversion afterwards.

How to calculate area in your browser

1. Select a shape: rectangle, triangle (base–height or three sides), circle, trapezoid or ellipse.
2. Choose the unit your measurements are in (m, cm, ft, in or yd).
3. Enter the dimensions the shape needs — the fields change to match.
4. Read the area and the formula used, and copy the result if you need it.

The five shapes and their formulas

Here's the full set the calculator handles, so you can see at a glance which measurements each one needs.

Shape	You provide	Formula
Rectangle	length, width	l × w
Triangle	base, height	½ × b × h
Triangle (3 sides)	a, b, c	Heron's formula
Circle	radius	π × r²
Trapezoid	parallel sides, height	(a + b) ÷ 2 × h
Ellipse	two radii	π × a × b

The three-sides triangle mode is especially handy for irregular plots where you can measure edges but not the height. The tool also flags impossible inputs, such as three sides that can't actually form a triangle.

Key features

• Five shapes: rectangle, triangle, circle, trapezoid and ellipse
• Triangle by base–height or three sides (Heron's formula)
• Results in m², cm², ft², in² or yd²
• The exact formula shown alongside the result
• Validates impossible inputs before calculating
• 100% private, free and no sign-up

Try the Area Calculator now — it's free and runs entirely in your browser.

Frequently asked questions

How do I find a triangle's area from three sides?

Use Heron's formula: with s = (a + b + c) ÷ 2, area = √(s(s−a)(s−b)(s−c)). A triangle with sides 5, 6 and 7 has s = 9 and area √216 ≈ 14.7. The tool applies this automatically in three-sides mode.

What's the formula for a circle's area?

Area = π × r², where r is the radius. A 5 m radius gives π × 25 ≈ 78.54 m². If you only have the diameter, halve it first — a 10 m diameter circle has that same 78.54 m² area.

How do I find the area of a trapezoid?

Average the two parallel sides and multiply by the height: (a + b) ÷ 2 × h. Parallel sides of 6 m and 10 m with a 4 m height give 8 × 4 = 32 m².

How many square feet is a 12 by 14 room?

Multiply length by width: 12 ft × 14 ft = 168 ft². For flooring or paint, add 5–10% for cuts and waste. Choose rectangle mode and the ft unit to compute any room size.

How do I convert square metres to square feet?

One square metre is about 10.7639 square feet, because 1 m = 3.28084 ft and area scales with the square. A 50 m² apartment is roughly 538 ft². You can also re-enter measurements in feet to get ft² directly.

Related free tools

• Unit Converter — switch between units before or after
• Scientific Calculator — for π, roots and powers
• Percentage Calculator — add waste percentages easily
• Distance Calculator — measure distances between points

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