ClarityKitFind a tool
Geometry

Triangle Inradius Calculator

Find the radius of a triangle’s inscribed circle from its three side lengths.

Use consistent dimensionsArea and volume units explained below
Geometry desk
Geometry desk

Match each dimension to the shape and keep units consistent.

See the method

Set the dimensions

Runs on your device

Your measurement

Your result

Let’s calculate.

Use the Calculate button to see your result.

Review the method below for assumptions and conventions.

How to use this tool

  1. Enter side a, side b, side c.
  2. Select Calculate to view the result.
  3. Check the method and assumptions below before using the result.

The method, explained

Use Heron’s area A=sqrt[s(s−a)(s−b)(s−c)], then inradius r=A/s.

A WORKED EXAMPLE

Using side a = 3 units, side b = 4 units, side c = 5 units, the result is 1 units. Change these example inputs to match your task; use the method above to check each step.

Understanding your result

Positive side lengths satisfying the strict triangle inequality. The incircle is tangent to all three sides.

What to keep in mind

Positive side lengths satisfying the strict triangle inequality. The incircle is tangent to all three sides. Use the indicated units consistently. Ideal shapes are assumed; dimensions must describe the same object. Display rounding does not increase measurement precision.

Common questions

How do I use this triangle inradius calculator?

Find the radius of a triangle’s inscribed circle from its three side lengths. Enter side a in units, side b in units, side c in units. The starting example is editable; use values for the same system or project.

Which assumptions affect this result?

Positive side lengths satisfying the strict triangle inequality. The incircle is tangent to all three sides.

Methodology maintained by ClarityKit. How these tools are built and checked.