Perimeter Calculator

Perimeter is the total distance around the outside of a 2D shape, measured in linear units. For a rectangle 8 by 5, the perimeter is 26 units. For a circle, the perimeter has its own name: circumference. A circle of radius 5 has a circumference of about 31.416 units.

Perimeter is the distance around a polygon (a shape with straight sides). Circumference is the distance around a circle. Both measure the boundary of a 2D shape; they are just named differently for historical reasons.

Rectangle, triangle (three sides), circle (circumference), trapezoid (all four sides), parallelogram (base and slant side), and regular polygon (number of sides and side length). For variations like irregular polygons or shapes with curved sides, use the shape-specific calculators.

Rectangle: P = 2 × (length + width). Triangle: P = a + b + c. Circle: C = 2 × π × r. Trapezoid: P = base 1 + base 2 + side 1 + side 2. Parallelogram: P = 2 × (base + slant side). Regular polygon: P = n × s.

Whatever unit you used for the inputs. If you entered feet, the perimeter is in feet. The calculator does not convert units; keep all inputs consistent.

Not directly. For an irregular polygon, sum the side lengths yourself; the perimeter is just the total. For curved boundaries that are not a circle (ellipse, parabola, irregular curve), the formula is more involved and is not handled by this hub.