What is the Difference Between Radius and Diameter?

The difference between radius and diameter is that a radius is a distance from a circle’s center to its periphery, while a diameter refers to the circumference of a circle.

Radius and diameters are important parameters for resolving circle circumference and area calculations.

So, let’s look at the definitions of radius and diameter in more detail below for better understanding.

What is Diameter?

What Is Diameter

The circle’s diameter is measured from one edge to the other, passing through the center.

The simplest technique to measure diameter is with a ruler.

If you have a ruler, the simplest way to start would be to measure the diameter by running the ruler from the circle’s center to its outermost point, which would be the diameter.

A circle’s diameter is measured around it when two points are drawn through its center.

Diameters are a crucial value for computations involving circles.

Contrary to triangles, rectangles, and squares, circles are difficult to measure by using a ruler to determine their circumference. 

Therefore, it is impossible to calculate the area using side measurements. Instead, we define a circle’s circumference and area using its diameter measurement.

The longest chord in a circle is the diameter.

The circle’s center must be where a straight line connecting its opposite edges passes.

A line is referred to as a chord if its ends still fall on the circular arc despite not passing through the center.

All chords are diameters, but not all diameters are chords.

A different definition might be that the diameter equals twice the radius. The equation that represents this claim is as follows:

Diameter = 2 x radius

The formula can also be expressed as:

d = 2r

Where the diameter is d and the radius is r.

What is Radius?

What Is Radius

The radius is the distance inside the circle from its periphery to its center. The circle’s diameter is calculated by dividing the radius by two.

Radius is the separation between any two points on a circle’s circumference.

A circle’s radius is equal to half of its diameter.

This is the distance of any two points along the circle’s perimeter from the center of the circle.

The formula of the radius is r = D/2

Difference Between Radius and Diameter

The main difference between diameter and radius is that the radius is the separation between a circle’s center and its edge. 

On the other hand, the diameter is the distance along the circle’s circumference from one point to the opposite point, measured through the circle’s center.

The lowercase letter r denotes the radius. A diameter is indicated by the uppercase letter D.

A circle’s diameter is constant from beginning to end. Only from the edge to the center does the radius extend.

For circles, the diameter and radius are crucial measurements needed to finish the calculations for the circumference and area.

The radius is the distance along a line drawn from one point on the circle to its center.

While the diameter is the distance along a line that connects all of the points on a circle and goes through its center.

Half of the diameter is the radius, and the diameter is equal to two times that length.

The diameter of a circle is the longest line that can be drawn through its center, and the radius is the line that extends from any point on the circle’s circumference to its center.

We can create formulas for the radius and diameter using the letters r and D, respectively.

Formula for Radius: r = D/2

Formula for Diameter: D = 2r

What is the Difference Between Radius and Diameter?

Difference Between Radius And Diameter

1. Difference in Length


The radius’s length is less than the circle’s diameter.


The diameter length is twice as long as the circle’s specified radius. 

It can start from every point along the circle’s edge, but the ending point differs between a chord and a diameter because they are each at the opposite edge of the same circle.

2. Difference in Symbol

Symbols are used to distinguish between radius and diameter.


The letter “R” stands for the symbol for the radius. That is R, which stands for radius simply.


Diameter Is Denoted by The Letter “D.”

3. Difference in Formula


“R = D/2” is the formula for calculating a circle’s radius. This indicates that the radius value is obtained by halving the diameter.


“D = 2r” is the formula for the circle’s diameter. The length of the diameter is calculated by multiplying the radius by two. Circle problems can be solved quickly using these two formulas.

4. Difference in Edge and Points


The radius starts at the circle’s center point and touches the circle’s edge only once.


In contrast, the diameter touches the circumference twice at different points compared to the radius when connecting points and edges.

Radius Vs Diameter

Highlighting the comparison between diameter and radius in the following chart:

The radius is the distance measured from a circle’s center to its edge.The circle’s diameter is its entire length, from one side to the other, from the edge to the center.
R or r is used to represent radius.D or d is used to represent diameter.
A circle’s radius is the distance it takes to reach any given point from its center.Through the center and from edge to edge, the diameter runs.
The formula for radius is r = d x 2.The formula for the diameter is d = 2r.


The key difference between radius and diameter is that the radius is the range a circle travels from its center to any given point. In contrast, the diameter is the entire “width” of the circle. Therefore, D = 2r OR r = D/2.

Read more: What is the Difference Between Tablets and Capsules?

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