Online Protractor

Enter an angle to see it drawn on a protractor, along with its type, radians and complementary and supplementary angles.

How to use the Online Protractor

Enter an angle between 0° and 180°.
See it drawn on the protractor.
Read its type and related angles.

How it works

A protractor measures angles in degrees from 0° to 180°. Angles under 90° are acute, exactly 90° is a right angle, between 90° and 180° is obtuse and 180° is a straight angle. Complementary angles add to 90°; supplementary angles add to 180°. To measure a real angle, place the protractor’s center on the vertex and its baseline along one arm.

Angle types

Angle	Type
0°	Zero angle
1°–89°	Acute
90°	Right
91°–179°	Obtuse
180°	Straight
181°–359°	Reflex

Frequently asked questions

How do I use a protractor?

Put the center hole on the angle’s vertex, line the baseline up with one arm and read where the other arm crosses the scale.

What is the supplement of 45°?

135°.

What is a right angle?

Exactly 90°.

Can a protractor measure 270°?

A half-circle protractor measures up to 180°; measure 360° minus the smaller angle for reflex angles.

How do I measure an angle larger than 180°?

Measure the smaller angle on the other side and subtract it from 360°.