Diameter Calculator
Calculate the exact mathematical diameter of a perfect circle. Reverse-solve from Circumference, Area, or Radius instantly, complete with algebraic step-by-step proofs.
How to Calculate Diameter
The diameter is the fundamental building block of all circular geometry. Because all three major circle properties (Radius, Area, Circumference) are mathematically locked together by the constant Pi (π), knowing ANY of these measurements allows you to algebraically trace your way back to the diameter.
From Radius
The radius connects the center to the edge. The diameter connects edge-to-edge *through* the center, making it exactly twice as long.
From Circumference
Pi (π) literally means "the ratio of a circle's circumference to its diameter". Therefore, divide the circumference by Pi.
Extracting Diameter from the Area
This is the hardest metric to manually calculate because the standard Area formula `A = π × r²` contains an exponent, meaning we have to use a square root to work backwards.
Area Formula Reversal
Step 1: Divide the total area by Pi.
Step 2: Take the square root of that number (this isolates the naked Radius).
Step 3: Multiply by 2.
Frequently Asked Questions
Studying for Geometry Exams?
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