Perimeter is the total distance around a two-dimensional shape. For a circle, the equivalent term is circumference.

Can this calculator find area too?

For rectangles, squares, triangles, circles, and parallelograms, the calculator shows area when the required dimensions are available.

What units does perimeter use?

Perimeter uses the same linear unit as the dimensions, such as centimetres, feet, or metres.

What is the perimeter of a rectangle?

Add the four sides, or use P = 2(l + w). A rectangle 5 units by 3 units has a perimeter of 16 units.

What is the difference between area and perimeter?

Perimeter measures the distance around a shape in linear units. Area measures the surface inside it in square units. A 5 by 3 rectangle has perimeter 16 and area 15.

Can I share a calculation?

Yes. Use Share to copy a URL containing the current calculator values, then open that link on another device or send it to someone else.

Perimeter Calculator – Area, Circle & Triangle Perimeter

A clear answer before the details

Perimeter is the sum of all outside side lengths. A circle has circumference C = 2πr, while a rectangle has perimeter P = 2(l + w).

Find the distance around a shape

A perimeter calculator adds the outside side lengths of a two-dimensional shape. The rectangle perimeter is P = 2l + 2w, a triangle perimeter is a + b + c, and a circle perimeter is more commonly called circumference, C = 2πr. Use the shape selector, enter consistent dimensions, and read the linear-unit result. This is different from area, which measures the surface inside the boundary.

When an area and perimeter calculator helps

An area and perimeter calculator is useful for planning fencing, trim, borders, walking paths, garden beds, flooring, and paint. The perimeter tells you how much material follows the edge; the area estimates how much surface fills the shape. For a rectangle measuring 5 m by 3 m, perimeter is 16 m and area is 15 m². Keep linear units for perimeter and square units for area.

Formula guide

The key equations are separated below. Start with the calculator mode, then choose the shape or model that matches your problem.

Rectangle

P = 2(l + w)

Add two lengths and two widths.

Square

P = 4s

Four equal sides of length s.

Triangle

P = a + b + c

Add all three side lengths.

Circle circumference

C = 2πr

A circle’s perimeter is called circumference.

Trapezoid

P = a + b + c + d

Add both bases and both legs.

Parallelogram

P = 2(a + b)

Opposite sides are equal.

Worked example

A rectangle measuring 5 by 3 has P = 2(5 + 3) = 16 linear units and area 5 × 3 = 15 square units.

Formulas for common use cases

Use the matching equation for the problem you are solving, then enter its variables in the calculator above.

Fencing and borders

material needed = perimeter

Use linear units for material around an edge.

Area and perimeter

rectangle area = l × w

Area measures the inside, while perimeter measures the boundary.

Circle from diameter

C = πd

Use diameter d when radius r is not given.

How to use this calculator

Choose a shape.
Enter each required side, radius, or dimension.
Review the perimeter and optional area.
Follow the area link when you need a separate surface calculation.

Where it helps

Perimeter helps estimate fencing, trim, borders, walking paths, wire, and material around a shape. The optional area result is useful when planning both the boundary and the amount of surface inside it. For a user-defined polygon, enter each side in order and the calculator adds them.

Common mistakes

Do not report perimeter in square units; it uses linear units. For a circle, diameter and radius are different inputs. Make sure all side lengths belong to the same shape and unit system before adding them.