Raio da Circunferência Circunscrita
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
R = abc/(4A)
About this calculator
The circumscribed circle radius calculator determines the radius of the circle that passes through the three vertices of a triangle. It uses the formula R = abc/(4A), where a, b, and c are the side lengths and A is the area. The result is useful in geometry, engineering, and design problems involving triangles inscribed in circles.
Simply input the three side lengths and the area. The calculator applies the formula directly, providing the circumradius. Ensure consistent units (e.g., centimeters for sides and square centimeters for area) for an accurate result. The formula derives from the law of sines and works for any triangle, as long as the area is known.
Use this calculator in scenarios like designing gears, calculating dimensions of triangular mechanical parts, solving school or college geometry problems, or in architecture to determine the circle circumscribing a triangular structure. It is especially helpful when you know the sides and area but not the circumradius.
Caution: verify that the entered area is positive and corresponds to the triangle with the given sides. The formula assumes a non-degenerate triangle (positive sides satisfying the triangle inequality). For right triangles, the circumradius equals half the hypotenuse, which can serve as a quick check.
Frequently asked questions
What is the circumscribed circle radius?
It is the radius of the circle passing through the three vertices of a triangle, also called the circumradius.
Do I need to calculate the area separately?
Yes, you need to provide the triangle's area. If unknown, compute it using Heron's formula or another method.
Does the formula work for any triangle?
Yes, as long as the triangle is non-degenerate (positive sides satisfying the triangle inequality).
What units should I use?
Use consistent units. If sides are in meters, area must be in square meters, and the radius will be in meters.
Can I use it for a right triangle?
Yes. For right triangles, the circumradius equals half the hypotenuse, which can be used to verify the result.