Circle Terminology
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Skills Application: Circle Terminology
Step-by-Step: Circle Terminology
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Early wheels were made from horizontal slices of a tree trunks, they served the purpose but they were clunky and lacked structural strength. Spoked wheels were invented in the Bronze Age (c3300–1300 BC) and allowed the construction of lighter and swifter vehicles. Soon after this, horse-drawn spoked-wheel war chariots were used for the greater part of three millennia.


The spoked wheel with a hub at the center looks like the sun with its rays, the Latin word “ray” became the name for this new device “the spoke”. This is where the math word “radius” comes from, “a line in the direction of a spoke”, that is from rim to hub.

Circle Terminology

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Running with Pi

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Mathematically, a circle is a closed curve representing the set of points some fixed distance from a given point called the center. In the circle below the center point is labelled "O".
  episode 13

Radius: We call radius the distance between the center of a circle and any point along the circle. It is represented by the letter r.

Diameter: The diameter of the circle is the distance between two points along the circle measured through the center. It is represented by the letter d.

There exists an interesting relationship between the diameter and the radius of a circle. The diameter is two times the radius. Another way to say it is that the radius is half the diameter. So if you know the radius of a circle you can find the diameter by doubling it and vice versa. That is

d = 2r            or              r = d ÷ 2


The perimeter of a circle is called circumference. It is the distance around the circle. For all circles, the ratio of the circumference to the diameter, the distance around the circle to the distance across, is the same number. The value of this ratio has been given the label π, the Greek letter “pi.” The value of π is approximately 3.14


Ratio = circumference ÷ diameter = 3.14159 = π


A Short Review

Circle`s perimeter = circumference

Origin = circle`s center point

Diameter = straight across through the origin

Radius = half the diameter

Pi (π) = circumference ÷ diameter

GetMath Worksheet Level1 novertspaac

Worksheet: Level 1

The operations used are clearly specified. Only one type of mathematical operation is used in a task.

Worksheet: Level 1 Sample Question

Example: List the terms from shortest length to longest:

  • radius
  • origin
  • circumference
  • diameter

Worksheet: Level 1 Answer Key


  1. origin
  2. radius
  3. diameter
  4. circumference

Download Worksheet: Level 1

GetMath Worksheet Level2 novertspaac

Worksheet: Level 2

Tasks involve one or two types of mathematical operation. Few steps of calculation are required.

Worksheet: Level 2 Sample Question


True or False?

1.  A radius is always longer than the diameter.


2.  Which 2 circle parts is Pi (π) a quotient of?

Worksheet: Level 2 Sample Answer


1. False, the radius is always shorter. (of the SAME circle)

2. Circumference and diameter

Download Worksheet: Level 2


Worksheet: Advanced Level

Tasks involve multiple steps of calculation. Advanced mathematical techniques may be required.

Worksheet: Advanced Level


Measurement math connections for trades & technology

Circumference is a type of Perimeter, which is a type of Length or Distance. It is implied that Circumference is a Length that completes an enclosed loop or circuit. Partial Circumferences have different names, as seen in the table below.

Circumference can be measured in Metric or Imperial units, many of these are used only in specific industries. For example the perimeter of Earth in nautical miles is mostly applicable to sea travel, navigation and aviation. The perimeter of a piston ring inside a cylinder bore is only used in automotive context.

Property of matter being measured:
possible synonyms
Unit of measure
Imperial & US
Distance (1-D)
in straight line:
straight lines of circles:
loops (full or part) :
length, width, height,
depth, thickness, gauge
side, edge, strain
L or l, w, h,
d, th, ga.
s, e,  e (Greek epsilon)
and other prefixes (kilo, centi, …)
mile, fathom
furlong, yard
feet, inch
mi, fm
fur, yd
ft, in



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