Area Calculator
Calculate the area of rectangles, circles, triangles, trapezoids, and more.
Written by Golam Rabbani, Founder & Lead Engineer
How to use this area calculator
- Select the shape: Rectangle, Circle, Triangle, Trapezoid, or Parallelogram.
- Enter the required dimensions — Length and Width, Radius, Base and Height, or Side a, Side b, and Height.
- Choose a unit (m², cm², ft², or in²) from the unit toggle.
- Press Calculate to see the area and perimeter in the result panel.
- Use Copy to save the result to your clipboard, or Reset to clear all inputs.
About this area calculator
The area calculator finds the area — and where applicable the perimeter — of five common shapes: rectangle, circle, triangle, trapezoid, and parallelogram. Enter your dimensions, pick a unit, and the tool returns the result instantly without any page reload.
Each shape uses its standard geometric formula. Rectangle: Area = length × width. Circle: Area = π × radius². Triangle: Area = ½ × base × height. Trapezoid: Area = ½ × (side a + side b) × height. Parallelogram: Area = base × height. For rectangles and circles the tool also calculates the perimeter (2 × (length + width) and 2 × π × radius respectively). When you switch units the calculator converts the stored dimensions using the exact conversion factor for that unit pair, so your numbers stay consistent without manual re-entry.
As a worked example, entering a rectangle with a length of 8 m and a width of 5 m gives an area of 40 m² and a perimeter of 26 m. If you then switch to cm² the result updates to 400,000 cm² and 2,600 cm. This tool is useful for home improvement projects, architecture students, and anyone who needs a quick geometry reference.
FAQ
- What is an area calculator and what shapes does it support?
- An area calculator computes the two-dimensional space enclosed by a shape. This tool supports five shapes: rectangle, circle, triangle, trapezoid, and parallelogram.
- What formulas does the area calculator use?
- Rectangle: length × width. Circle: π × radius². Triangle: ½ × base × height. Trapezoid: ½ × (side a + side b) × height. Parallelogram: base × height. Perimeter is calculated for rectangles and circles only.
- How accurate are the results?
- Results are mathematically exact given your inputs and are displayed to four decimal places. For practical construction or engineering work, verify your measurements independently — digital rounding at four decimal places is negligible for everyday use.
- What happens if I enter a zero or negative dimension?
- The tool shows an error message and does not calculate. All dimensions must be positive numbers greater than zero for a result to appear.
- Does this tool store my measurements?
- No. The area calculator runs entirely in your browser and nothing is sent to a server. Closing or refreshing the page clears all inputs.
- Is the area calculator free?
- Yes. It is free to use with no account, no signup, and no usage limit.