Area Calculator
Calculate the area of a rectangle, triangle, circle, trapezoid or parallelogram.
Results update as you type.
About this calculator
An area calculator finds how much surface a 2D shape covers. Pick the shape, enter its dimensions, and it returns the area — and, where the sides are known, the perimeter or circumference. Only the fields the chosen shape actually needs are used; the rest are ignored.
Each shape has its own formula: a rectangle is length × width, a triangle is ½ × base × height, a circle is π × radius², a trapezoid is ½ × (base₁ + base₂) × height, and a parallelogram is base × height. For a rectangle 5 long and 4 wide the area is 5 × 4 = 20 and the perimeter is 2 × (5 + 4) = 18; a triangle with base 6 and height 4 has area ½ × 6 × 4 = 12; a circle of radius 5 has area π × 25 ≈ 78.54. Perimeter is shown for rectangles and circles, but not for triangles, trapezoids or parallelograms, whose slanted sides are not entered.
Area calculations are needed for flooring, paint, fabric, land, and any project measured by surface. Make sure all dimensions use the same unit, and the area comes out in that unit squared.
Frequently asked questions
How do you find the area of a triangle?
Area = ½ × base × height, using the perpendicular height. A triangle with base 6 and height 4 has area ½ × 6 × 4 = 12.
What is the area of a circle?
Area = π × radius². A circle of radius 5 has area π × 25 ≈ 78.54.
How do you find the area of a rectangle?
Multiply length by width. A rectangle 5 long and 4 wide has area 5 × 4 = 20.
What is the area of a trapezoid?
Area = ½ × (base₁ + base₂) × height, averaging the two parallel sides and multiplying by the height between them.
What is the area of a parallelogram?
Area = base × height, using the perpendicular height, not the slanted side length.
Why does the perimeter sometimes show a dash?
Perimeter is given for rectangles and circumference for circles. Triangles, trapezoids and parallelograms need their slanted side lengths, which are not entered, so their perimeter is left blank.
Which fields do I need to fill in?
Only the ones the selected shape uses. A circle needs just the radius; the width and height fields are ignored for it.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/area-of-a-shape/curl
curl "https://calculator.free/api/v1/area-of-a-shape/?shape=rectangle&a=5&b=4&h=3"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/area-of-a-shape/?" + new URLSearchParams({
"shape": "rectangle",
"a": "5",
"b": "4",
"h": "3"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.