Difference Between Circumference, Diameter And Radius

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What is Diameter?

The diameter is the length of the line through the center that touches two points on the edge of the circle. In other words, it is the full length of the circle running from the edge, through the midpoint, all the way to the other side. It can also be defined as the longest chord of the circle. Both definitions are also valid for the diameter of a sphere.

Diameter can be thought of as a straight line that goes through the center point of the circle. Diameter is typically denoted by the lowercase letter d or by the symbol ⊘.

What is Radius?

A radius of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin radius, meaning ray but also the spoke of a chariot wheel.

In other words, Radius is the distance from the center point to one edge of a circle. In other words, the radius of a circle is equal to half of the circle’s diameter. The plural of radius can be either radii (from the Latin plural) or the conventional English plural radiuses. The typical abbreviation and mathematical variable name for radius is R or r.

If an object does not have a center, the term may refer to its circumradius, the radius of its circumscribed circle or circumscribed sphere. In either case, the radius may be more than half the diameter, which is usually defined as the maximum distance between any two points of the figure. The inradius of a geometric figure is usually the radius of the largest circle or sphere contained in it. The inner radius of a ring, tube or other hollow object is the radius of its cavity.

What is Circumference?

The circumference is the perimeter of a circle or ellipse. That is, the circumference would be the arc length of the circle, as if it were opened up and straightened out to a line segment. More generally, the perimeter is the curve length around any closed figure.

Circumference can also be described as the distance around a circle or any curved geometrical shape. It is the one-dimensional linear measurement of the boundary across any two-dimensional circular surface. It is denoted in mathematics by the capital letter C.

It is possible to relate diameter to circumference by using the formula:

Circumference=π×diameter

In other words, circumference of a circle is the product of the constant π and the diameter of the circle. A person walking across a circular park, or a circular table to be bordered requires this metric of the circumference of a circle. The circumference is a linear value and its units are the same as the units of length.

Circumference vs Diameter vs Radius

BasisCircumferenceDiameterRadius
DescriptionIt is the perimeter, or distance around a circle.It is a straight line that goes through the center point of the circle. It is the distance from the center point to one edge of a circle. 
EtymologyComes from Latin word circumferens, meaning “carrying around”).From Greek word: diametros, (dia), meaning “across, through” and (metros) meaning measure.Comes from the latin radius, meaning ray but also the spoke of a chariot wheel.
AbbreviationIt is denoted by letter C or lower case c.Denoted by the lowercase letter d or by the symbol ⊘.Typical abbreviation for radius is R or r.
FormulaC=π×diameterd=2rr=d/2

Key Takeaways

  • The diameter is defined as twice the length of the radius of a circle. The radius is measured from the center of a circle to one endpoint on the boundary of the circle, whereas, the distance of diameter is measured from one end of the circle to a point on the other end of the circle, passing through the center.
  • The radius (r) is the length of the line segment from the center of the circle to an endpoint on the circle.
  • Circumference is the perimeter, or distance around a circle.
  • Diameter=2×radius
  • The circumference of a circle is equal to the circle’s diameter multiplied by pi (π). Circumference=π×diameter