Area Calculator
Calculate the area of a rectangle, circle, or triangle.
Formulas used
Rectangle: length × width. Circle: π × radius². Triangle: ½ × base × height.
Choosing the right shape and units
Make sure both dimensions are in the same unit before calculating — mixing feet and inches, or meters and centimeters, will produce an incorrect area. Convert everything to one consistent unit first.
For irregular shapes not covered here (like trapezoids or complex polygons), break the shape into simpler rectangles, triangles, or circles, calculate each area separately, then add them together for the total.
A worked example
A rectangular room 12ft by 15ft has an area of 180 square feet — useful for flooring or paint coverage estimates.
A circular pool with a 4ft radius has an area of pi times 4 squared, approximately 50.3 square feet, while a triangular garden bed with a 6ft base and 4ft height has an area of one-half times 6 times 4, or 12 square feet.
Area formulas for common shapes
Beyond the three shapes covered here, other common area formulas include a trapezoid (½ × (base1 + base2) × height), a parallelogram (base × height), and a regular polygon (more complex, involving the number of sides and apothem) — rectangle, circle, and triangle formulas cover the large majority of everyday area calculations.
Units matter as much as the formula — always ensure both dimensions are in the same unit before calculating, and remember that area is always expressed in square units (like square feet or square meters), reflecting its two-dimensional nature.
Frequently asked questions
What does dimension 2 mean for a circle?
It's ignored — only dimension 1 (the radius) is used for circle area calculations.
How do I calculate area for a shape not listed here?
Break irregular shapes into combinations of rectangles, triangles, and circles, calculate each area, then sum them — this works for most real-world irregular shapes.
What's the difference between area and perimeter?
Area measures the space enclosed within a shape (in square units), while perimeter measures the total distance around the outside edge (in linear units) — they answer different questions entirely.
Why is area always in 'square' units?
Because area measures two-dimensional space — multiplying two length measurements together produces a unit that's inherently squared, like square feet or square meters.