Perimeter Calculator
Calculate the perimeter of 10 shapes including square, rectangle, triangle, circle, and polygon. Metric and imperial units with conversions.
Select a shape and enter dimensions.
Perimeter Calculator: Find the Perimeter of Any Common Shape
Perimeter is the total distance around the boundary of a two-dimensional shape, measured in linear units such as meters or feet. This calculator computes the perimeter of ten common shapes and converts the result between units, which makes it useful for fencing a yard, edging a garden bed, framing a picture, or estimating trim and border strips. Select a shape, enter the side lengths or radius, and the exact perimeter appears instantly.
Rectangle: 2 × (length + width)
Triangle: a + b + c
Circle: 2 × π × r
Parallelogram: 2 × (a + b)
Trapezoid: a + b + c + d
Ellipse: π × [3(a + b) - √((3a + b)(a + 3b))]
Rhombus: 4a
Circle sector: 2r + (angle/360) × 2πr
Regular polygon: n × a
What Perimeter Means and Where It Is Used
Perimeter answers the question of how far it is around something. It tells a builder how much fencing a yard needs, a gardener how much edging borders a flower bed, and a framer how much molding wraps a picture. Because the math is universal, the same formulas apply whether you measure in meters or feet. The calculator keeps the full precision of pi so circles, ellipses, and sectors stay accurate.
Perimeter Versus Area
Perimeter and area describe different things. Perimeter is the distance around the edge and uses linear units like meters, while area is the surface inside and uses square units like square meters. A fence follows the perimeter; the lawn it encloses is the area. Two shapes can have the same perimeter but very different areas, which is why it matters to use the right measurement for the job.
Circles and Irregular Shapes
For a circle the perimeter is called the circumference, found with 2 × π × r, because a circle has no straight sides to add up. For shapes with straight edges you simply add every side. For an irregular outline, break it into segments you can measure, add the straight parts, and treat any curved part as an arc. The calculator handles the standard shapes so you only enter the measurements it asks for.
Tips & Recommendations
Perimeter is the distance around a shape in linear units; area is the space inside in square units. Pick the one your project needs.
A circle has no sides to add, so its perimeter (the circumference) is 2 × π × r. If you only know the diameter, that equals π × diameter.
Every side of one shape must use the same unit. Convert before you enter values, then let the tool show the conversions.
For a shape that is not in the list, measure each straight side and add them together to get the total perimeter.
Frequently Asked Questions
What is perimeter?
Perimeter is the total distance around the outside of a two-dimensional shape. You find it by adding the lengths of all the sides, or for curved shapes like a circle by using a formula. Perimeter is measured in linear units such as meters or feet, not square units, because it is a length and not an area.
What is the difference between perimeter and area?
Perimeter measures the distance around a shape, while area measures the surface it covers. Perimeter uses linear units like meters; area uses square units like square meters. A fence around a yard follows the perimeter, but the grass inside is the area. Two shapes can share the same perimeter yet have very different areas.
How do I calculate the perimeter of a circle?
The perimeter of a circle is called the circumference, and the formula is 2 times pi times the radius (2 × π × r). For a radius of 7, the circumference is about 43.98 units. If you know the diameter instead, the circumference equals pi times the diameter, since the diameter is twice the radius.
What do I need to find a triangle's perimeter?
You need the lengths of all three sides, because the perimeter of a triangle is simply side a plus side b plus side c. Unlike the area, the base and height are not enough. The three sides must also satisfy the triangle inequality, meaning any two sides added together must be longer than the third side.
What units is perimeter measured in?
Perimeter is always a length, so it uses linear units: meters, centimeters, millimeters, inches, or feet. Conversions are linear, so one meter equals 100 centimeters and about 3.28 feet. This calculator shows your result in the unit you choose and converts it to meters, centimeters, and feet automatically.
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