Circle calculator

The online calculator can also help in finding the area, diameter and circumference of a circle.


Definition of a circle: A circle is a closed plane curve which divides the plane into two regions, an interior and an exterior, such that every point on the curve is at a fixed distance from a fixed point. The fixed point is called the center and the distance is called the radius. The circle with center C and radius r is the set of all points in the plane such that the distance from a point P to the center C is r. This set is denoted by O(C, r).

Origins of the circle date back to the Neolithic period. Neolithic people used circles to mark events like seasons, solar cycles (solstices and equinoxes), and were used to measure periods of time. The circular shape was often associated with life, fertility, and the sun. Let's break down the definition of circle to further understand the concept. A circle is a shape with a single curve where all lines tangent to the curve (its circumference) are equal in length, and where all points on the curve lie an equal distance from a single point within the curve.

Circle calculator is a simple online tool to calculate the area of a circle given the radius. The calculator can be used to find the area of a circle from any sized radius. After typing the required input you will see the results in the form of a circle area equivalent to the radius you have entered. The formula for calculating the area of a circle is: A = πr² where r is the radius.

circle calculator

Circle Formula:-

  • Area of circle = πr²
  • Circumference of circle = 2πr
  • diameter of circle = 2r

Centre of circle ◯

The fixed point is called the centre in thr given picture 'o' is the centre of the circle.

A circle is a regular shape and is considered one of the most basic shapes in math and geometry. A circle can be defined as a regular curve in a plane. The curve is the locus of a point that is at a constant distance from a given point called the centre. The distance between the centre and the point is called the radius and the point is called the centre. The basic formula for a circle is:

Radius of circle ◯

A radius is the fixed distance from a circle's center. The radius is a non-changing distance from a circle's center. If a circle is perfect, then the radius will always be the same. However , in the real world, a radius can change. A radius can be measured from an infinite amount of points, but there is always a fixed distance from the center of the circle.  There are many uses for a radius, but it can be used to find the circumference and area of a circle.

A radius of a circle is a straight line from the center of a circle to its edge. Back when the Egyptians were making circles, they didn't have a machine that could cut straight lines into a circle. So they measured a part of a circle with a stick that had a length of a certain number of units on it, and then they drew a straight line from a certain point on a right angle triangle to a point on a circle. This distance from the center of the circle to the circle's edge is called a radius.

Diameter of circle ◯

A diameter of a circle is a line segment passing through the center and joins the two points on the circle. A diameter is the longest distance between two points on the circle. The distance between any two points on a circle is always half the diameter. A diameter is usually denoted by the symbol d.

Diameter = 2 x radius

Diameter of circle

Circumference of circle ◯

The word circumference means the length around a circle or sphere. We usually just say circumference instead of length. There is an exact mathematical formula for measuring circumference. But, most people don't use this formula. Instead, they use a basic unit of measure called the yardstick or ruler. The circumference of a circle is calculated by multiplying the length (in units of measurement like inches or centimeters) times Pi (which is approximately 3.14). A foot long ruler has twelve inches, which means it has twelve units. So, we multiply the twelve units by the Pi and we get the circumference of a foot long ruler: (12 inches times 3.14) equals (36.96 inches).

Circumference = 2π x radius

Circumference of a circle

How to use this circle calculator ❓

Enter only radius value in the proper input field and then click calculate, you see calculate the value in answer box with formula but if you want to enter another value so first clear the entered value then after entering new radius value . 😉

See here table of circle value ⭐

Radius(Unit) Diameter Area Circumference
1 2 3.14159 6.28319
5 10 78.53982 31.41593
10 20 314.15927 62.83185
20 40 1256.63706 125.66371
50 100 7853.98163 314.15927

How to solve circle problem❓

Example.1:-Circle of Radius = 10 cm , find area of circle, circumference of circle and diameter of circle

Area of circle = πr² = 314.15927 cm²

Circumference of circle = 2πr = 62.83185 cm

Diameter of circle = 2r = 20 cm