Perimeter Calculator

What Is a Perimeter Calculator?

A perimeter calculator determines the total distance around the outside of a two-dimensional geometric shape. It uses the appropriate mathematical formula for the selected shape and returns the perimeter based on the measurements entered.

This tool is useful for students, teachers, DIY projects, construction planning, landscaping, design and everyday measurements. It can calculate the perimeter of rectangles, squares, triangles, circles and regular polygons without requiring manual calculations.

Why Use the Perimeter Calculator?

The calculator provides a simple way to work out perimeter measurements while reducing the need to apply formulas manually.

How to Use the Perimeter Calculator

Select the shape you want to measure, enter the required dimensions and calculate the perimeter.

1. Select a shape — Choose a rectangle, square, triangle, circle or regular polygon.
2. Enter the measurements — Enter the dimensions required for the selected shape using the same unit of measurement.
3. Calculate the perimeter — Select the Calculate Perimeter button to perform the calculation.
4. Review the result — The calculated perimeter and formula used will be displayed below the calculator.

How to Calculate Perimeter

Perimeter is the measurement of the complete boundary of a two-dimensional shape. For polygons, the perimeter is found by adding the lengths of all sides. Some shapes have simplified formulas because their sides or dimensions follow specific relationships.

For example, the perimeter of a rectangle is twice the sum of its length and width. A square has four equal sides, so its perimeter is four times the length of one side. A triangle's perimeter is the sum of its three sides. For a circle, the equivalent measurement is called circumference.

Rectangle, Square and Triangle Perimeters

A rectangle has two pairs of equal sides, so its perimeter is calculated as 2 × (length + width). A square has four equal sides and uses the formula 4 × side. For a triangle, add the three side lengths together. The side lengths must be expressed in the same unit before calculating the total.

Circle and Regular Polygon Perimeters

The perimeter of a circle is called its circumference. It can be calculated from the radius using 2 × π × radius. A regular polygon has equal sides, so its perimeter is the number of sides multiplied by the length of one side.

Perimeter Calculation Accuracy and Units

The calculator accepts positive numerical measurements, including decimal values. It does not require a particular unit because perimeter calculations are based on the numerical measurements provided. If the inputs are in centimetres, the result is in centimetres; if they are in metres, the result is in metres.

For accurate results, use the same unit for every measurement in a calculation. The calculator uses π for circle calculations and displays the result to a practical number of decimal places. Very small rounding differences can occur when working with irrational values such as π.

Frequently Asked Questions