Diameter of a Circle Calculator
Calculated Diameter:
How to Calculate the Diameter of a Circle
The diameter of a circle is a straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It is exactly twice the length of the radius. Understanding how to find the diameter is fundamental in geometry, engineering, and daily DIY projects.
Depending on what information you already have about the circle, you can use one of three primary formulas:
1. Calculating from Radius
If you know the distance from the center to the edge (the radius), simply multiply by two.
Example: If the radius is 7 cm, the diameter is 2 × 7 = 14 cm.
2. Calculating from Circumference
If you have the total distance around the circle (circumference), divide it by Pi (π, approximately 3.14159).
Example: If the circumference is 31.42 inches, the diameter is 31.42 / 3.14159 ≈ 10 inches.
3. Calculating from Area
If you know the total space inside the circle (area), divide the area by Pi, take the square root of that result, and then multiply by two.
Example: If the area is 78.54 sq ft, the diameter is 2 × √(78.54 / 3.14159) = 2 × √25 = 2 × 5 = 10 ft.
Why Knowing the Diameter Matters
The diameter is the "width" of the circle. You need it when determining if a round object will fit through an opening, calculating the size of a circular table, or selecting the right drill bit for a specific hole size. In technical fields, diameter is the standard measurement for pipes, cables, and mechanical parts.