Perimeter Calculator
Calculate perimeter for common 2D shapes including square, rectangle, triangle, parallelogram, rhombus, trapezoid, regular polygon, and circle circumference.
Perimeter for common 2D shapes
English search results for perimeter calculator expect a broad geometry helper: choose the shape, enter the side lengths or radius, and get the outside boundary length. For a circle, the boundary length is usually called circumference.
| Shape | Typical inputs | Output |
|---|---|---|
| Square or rhombus | One side | Perimeter |
| Rectangle or parallelogram | Two adjacent sides | Perimeter |
| Triangle | Three sides, one side, equal side and base, or two legs | Perimeter and computed side when needed |
| Trapezoid | Four sides | Perimeter |
| Regular polygon | Number of sides and side length | Perimeter |
| Circle | Radius | Circumference and diameter |
Core formulas
P is square perimeter; a is side length.
P is rectangle perimeter; a and b are adjacent sides.
P is triangle perimeter; a, b, and c are side lengths.
P is regular polygon perimeter; n is side count; a is side length.
C is circumference; r is radius.
Units and limits
Enter all lengths in the same unit. The result is a linear length, so it is shown in mm, cm, m, km, in, or ft, not in square units.
Frequently Asked Questions
Sources and References
Calculations are based on the listed reference sources. Links open in a new tab.
Related Tools
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