Inscribed Circle Calculator

Find the inradius of a triangle from its three sides.

Inradius 1

Triangle area 6

Formula: r = area ÷ s, where s is the semi-perimeter

Step-by-step with your numbers:

1. Values used:

2. Side a = 3

3. Side b = 4

4. Side c = 5

6. Inradius = 1

7. Triangle area = 6

Did we solve your problem today?

The inscribed circle is the largest circle that fits inside a triangle, touching all three sides.

The math behind it

The inradius is r = Area ÷ s, where s = (a + b + c)/2 is the semi-perimeter and the area is from Heron's formula.

Sides 3, 4, 5 → area 6, semi-perimeter 6, inradius 1.

Where is the centre?

At the incentre, where the triangle's angle bisectors meet.