How to use the triangle inradius and circumradius calculator
Find inscribed and circumscribed circle radii of a triangle. Enter side a, side b, side c in the fields above; the area, inradius, circumradius are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- a — Side a
- b — Side b
- c — Side c
Worked example
With side a = 13, side b = 14, side c = 15, the calculator gives area ≈ 84; inradius ≈ 4; circumradius ≈ 8.125.
Frequently asked questions
What is the formula for the triangle inradius and circumradius calculation?
Area = √(((a+b+c) / 2) × ((a+b+c) / 2-a) × ((a+b+c) / 2-b) × ((a+b+c) / 2-c)). Inradius = [Area] / ((a+b+c) / 2). Circumradius = a × b × c / (4 × [Area]). Here a is side a, b is side b, c is side c.
What inputs do I need for the triangle inradius and circumradius calculator?
You need side a, side b, side c. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.