Calculate circular diameter from radius, circumference, or area.
Known Value
Input Value
d = 10
Circle Properties
10
Diameter (d)
Radius (r)5
Circumference (C)31.4159
Area (A)78.5398
About this calculator
What is the Diameter?
The diameter is a straight line segment that passes through the center of a circle and whose endpoints lie on the circle. It is exactly twice the length of the radius and represents the widest part of the circle.
💡
Pro Tips
If you know the radius, just multiply by 2.
If you know the circumference, divide by π (approx. 3.14159).
If you know the area, divide by π, take the square root, then multiply by 2.
!
Fun Facts
"The word 'diameter' comes from the Greek 'dia' (across) and 'metron' (measure)."
"Any angle inscribed in a semi-circle is a right angle (Thales' Theorem)."
"The diameter is the special case of a chord that passes through the center."
