Perimeter Calculator

Choose a rectangle, square, triangle, circle, or regular polygon and calculate its perimeter instantly.

Shape

First value

Second value

Third side

PerimeterLinear units

Perimeter reverse solver

Calculate a perimeter or solve a missing dimension from a target perimeter while keeping the geometry assumptions explicit.

ShapeTarget perimeterDimension ADimension BDimension C / sides

—Perimeter

—Reverse-solved dimension

Ready.

Use consistent measurements and valid geometric assumptions

Keep linear inputs in a consistent unit, verify that side lengths or coordinate points can form the stated shape, and treat sketches as explanatory unless explicitly marked to scale. Coordinate formulas can become unstable for nearly degenerate shapes, so invalid or nearly collinear inputs are rejected rather than silently returning misleading values.