Select a shape and enter the required dimensions to see the area and perimeter here.
FAQ
Which shapes can I calculate?
The tool covers rectangles, circles, triangles, trapezoids, and regular polygons. Enter the dimensions requested for each shape to get area and perimeter.
Do I need to specify units?
Use whatever units you prefer. The calculator keeps everything consistent, so if you enter centimetres the area will be in square centimetres and the perimeter in centimetres.
What do I enter for a regular polygon?
Provide the number of sides (3 or more) plus at least one of the following: side length, circumradius, or apothem. Missing values are derived automatically.
Which shape should I choose first?
Choose the shape that matches the known dimensions you have. For a polygon, decide whether side length, apothem, or circumradius is the measured value before entering numbers.
Why can area or perimeter differ from another worksheet?
Different tools may use rounded intermediate values, a different polygon input, or a different unit label. Compare the displayed formula and the raw dimensions before comparing final values.
How to use the 2D geometry calculator effectively
Start from the measured dimensions
Select the figure that matches your sketch, then enter the dimensions you actually know. For regular polygons, the side length, apothem, and circumradius describe different measurements.
Keep units consistent
The calculator does not convert units automatically inside a shape. If the length is in centimetres, the perimeter is in centimetres and the area is in square centimetres.
Use-case sequence
A practical sequence is: draw the shape, label the known dimensions, choose the matching input mode, then verify the formula line before copying the result.
Common mistakes to avoid
Do not mix radius and diameter, confuse apothem with side length, or compare areas from different unit systems without converting them first.
Interpretation guidance
Area answers a covering question, while perimeter answers a boundary question. Keep those two meanings separate when estimating paint, fencing, fabric, or worksheet examples.