Circumscribed Circle Calculator
Find the circumcircle radius, diameter, circumference and area from three triangle sides.
Formula
R=abc/(4Δ), Δ=√[s(s−a)(s−b)(s−c)], s=(a+b+c)/2; d=2R, C=2πR, A=πR².
Side a: 3 cm · Side b: 4 cm · Side c: 5 cm · Circumradius ≈ 100×(3 cm × 0.01 m/cm)×(4 cm × 0.01 m/cm)×(5 cm × 0.01 m/cm)÷(4×(0.0006)) · Diameter ≈ 2×(2.5) · Circumference ≈ 2×pi×(2.5) · Circle area ≈ pi×(2.5)^2
How to use
- Enter all three side lengths.
- Choose units and use a valid triangle.
- Read the circumcircle measurements.
Examples
- A 3–4–5 cm triangle has circumradius 2.5 cm.
Frequently asked questions
Which triangles are valid?
Each side must be shorter than the sum of the other two. Nearly degenerate triangles are rejected.
Is this an incircle?
No. The circumcircle passes through the three vertices.
Can I find the center coordinates?
Use the circumcenter calculator with the three vertex coordinates.
Sources
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