How do I calculate the area of a rectangle?

Multiply length by width: A = l × w. A room 12 ft long and 10 ft wide has an area of 120 square feet. Area is always expressed in square units because it measures two dimensions.

What is the formula for the area of a circle?

A = πr², where r is the radius (half the diameter). A circle with a 5 cm radius has an area of about 78.5 cm². If you only know the diameter, divide it by 2 before squaring.

How do I find the area of a triangle?

The standard formula is A = ½ × base × height, where the height is measured perpendicular to the base. If you only know the three side lengths, use Heron's formula: compute the semi-perimeter s, then A = √(s(s−a)(s−b)(s−c)).

How do I calculate the area of an irregular shape?

Break the shape into simple pieces — rectangles, triangles, and circle segments — calculate each area separately, and add them together. For an L-shaped room, for example, split it into two rectangles and sum the results.

Why does the unit of measurement matter for area?

Area scales with the square of the length unit, so unit conversions are easy to get wrong. One square meter is 10.76 square feet, not 3.28, and one square yard is 9 square feet. Always convert lengths to the same unit before multiplying.

Area Calculator

Calculate area of circles, rectangles, triangles, and other geometric shapes. Free, fast, accurate — no signup, mobile-f

Select Shape

Rectangle Dimensions

Length

Width

📐 Formula

Area = length × width

ℹ️ Shape Information

Type: Rectangle

Category: Quadrilateral

Description: Four-sided polygon with opposite sides equal and all angles 90°

Area

square units

Perimeter

linear units

Step-by-Step Solution

1Given: length = 10, width = 5

2Area = length × width = 10 × 5 = 50

3Perimeter = 2(length + width) = 2(10 + 5) = 30

How it works

Area measures the two-dimensional space a shape covers, in square units. Each shape has its own formula, but the calculator just applies the right one to your dimensions. For odd shapes, the trick is to split them into rectangles and triangles, find each area, and add them up.

Common area formulas

Rectangle = length × width        Triangle = ½ × base × height        Circle = π × radius²

length, width: sides of a rectangle
base, height: base and perpendicular height of a triangle
radius: distance from a circle's centre to its edge

Worked example

A room 12 ft long and 10 ft wide

Area = length × width = 12 × 10

Area = 120 square feet.

Good to know

Keep units consistent — mixing feet and inches gives a wrong answer. Convert first, then multiply.
Area is always in square units (ft², m²); a length × a length = a square unit.
For an L-shaped or irregular space, divide it into rectangles, compute each, and sum — far easier than one complex formula.