**How to convert from degree to radian or radian to degree? **

Using calculator:

→ What is 225 degree in radian?

We know that π = 180 degree so what we could do is using cross multiply:

**How to convert from degree to radian or radian to degree? **

Without using a calculator:

30 degree = π/6 radian

**Proof:** π = 180 degree

180/6 = 30

60 degree = π/3 radian

**Proof:** π = 180 degree

180/3 = 60

90 degree = π/2 radian

**Proof:** π = 180 degree

180/2 = 90

45 degree = π/4 radian

**Proof:** π = 180 degree

180/4 = 45

These are the different degrees of special right triangle and we can use them to determine the measure of triangles, in radian, without the use of calculator.

30-60-90 triangle

45-45-90 triangle