Definition
The distance around the outside edge of a circle. It is calculated by multiplying the diameter by pi (approximately 3.1416), or by multiplying the radius by 2 and then by pi.
Plain English
The total length of the line that forms a circle, measured all the way around its edge.
Context Anchor
Seen in maintenance work when measuring or calculating sizes of round parts, such as wheels, pulleys, cylinders, or tubing.
Derivation
From the Latin 'circum' meaning 'around' and 'ferre' meaning 'to carry.' Literally, 'to carry around' — the distance you travel when you go all the way around the outside of a circle.
Why Pilots Care
Maintenance calculations involving tire travel per revolution, propeller tip speed, pulley ratios, and similar rotating-part work all depend on circumference. Getting the formula wrong gives wrong answers in safety-critical work.
Analogy
If you wrap a tape measure around a coffee can one time, the length shown on the tape is the can’s circumference.
Intuition Check
Circumference does not mean the width across a circle. It means the distance around the outside edge.
Example Sentence 1
To find how far the aircraft travels in one full tire rotation, the technician calculated the circumference of the tire.
Example Sentence 2
Propeller tip speed depends on engine RPM and the circumference of the blade path.