Area Calculator
Calculate the area of a rectangle, circle, or triangle.
About the Area Calculator
Different shapes require different area formulas — this calculator covers the three most common shapes in home and construction projects: rectangles, circles, and triangles, switching formulas automatically based on your selection.
How It Works
For a rectangle, the calculator multiplies length by width. For a circle, it uses the radius squared multiplied by pi. For a triangle, it multiplies base by height and divides by two, matching the standard geometric formula for each shape.
Rectangle: L × W. Circle: π × r². Triangle: 0.5 × base × height.
Example
Scenario: A rectangle with dimensions 10 by 6.
Result: An area of 60 square units.
Assumptions & Limitations
- For circles, dim1 is treated as the radius, not the diameter — divide a known diameter by 2 before entering it.
- For triangles, dim1 is the base and dim2 is the height measured perpendicular to that base.
- Does not cover irregular polygons or compound shapes — break those into simpler rectangle, circle, and triangle sections and sum the results.
Frequently Asked Questions
Do I enter the radius or the diameter for a circle?
Enter the radius, which is half the diameter — if you only know the diameter, divide it by 2 before entering the value to get the correct area.
What is the height of a triangle for this calculation?
The height is the perpendicular distance from the base to the opposite vertex, not the length of one of the triangle's slanted sides.
How do I find the area of an irregular shape?
Break the irregular shape down into a combination of rectangles, triangles, and circle segments, calculate each piece's area separately, and add them together for the total.