Angle — 90° (Right Angle) — free printable diagram

What is a 90 degree angle?

A 90 degree angle (90°) is a right angle — the two arms are perpendicular and form a square corner. This diagram shows 90° opened between two arms meeting at a vertex.

Measure

90°

Type of angle

Right angle

Supplement (adds to 180°)

90°

Reflex angle on the other side

270°

In radians

π/2 (≈1.571)

Fraction of a full turn

1/4 of a turn

Interior angle of

a square

• A 90° angle is a right angle because the two arms are perpendicular and form a square corner.
• Angles on a straight line add up to 180°, so the angle next to this one measures 180° − 90° = 90°.
• Angles round a point add up to 360°, so the reflex angle on the other side of these arms measures 360° − 90° = 270°.
• To measure or draw it, put the centre of the protractor on the vertex where the two arms meet, line one arm up with the 0° mark, and read the scale that starts at 0° on that arm until you reach 90°.
• In radians, 90° × π/180 = π/2, which is about 1.571.
• Every corner of a square measures 90°, because its exterior angle is 180° − 90° = 90° and the exterior angles of any polygon add up to 360°.