Circle Calculator
Circle solve-for modes: one known measure yields r, d, C, and A with formulas shown.
Limitation: Educational geometry.
How to Use the Circle Calculator
Circle solve-for modes: one known measure yields r, d, C, and A with formulas shown.
Open the Circle calculator and read field labels.
Match the mode
Educational geometry.
What It Calculates
Circle solve-for modes: one known measure yields r, d, C, and A with formulas shown.
Worked Examples
Radius 5
Inputs
Result
d = 10; C ≈ 31.416; A ≈ 78.54.
Area 78.54
Inputs
Result
r = √(A/π).
Diameter 10
Inputs
Result
r = d/2.
Check your mode
Educational geometry.
Frequently Asked Questions
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Standard definitions with assumptions noted below.
Formula
Scientific Background
Standard geometry definitions with assumptions stated on-page. Educational only—not professional certification.
Sources & review
Circle Calculator documents the references behind its formulas and assumptions. Always treat results as educational estimates, not personalized professional advice.
Last reviewed
July 22, 2026
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