Regular Triangle (3 sides) — free printable diagram

How many sides does a triangle have?

A triangle is a three-sided shape — a polygon with 3 sides and 3 corners. An equilateral triangle has 3 equal sides and 3 equal angles of 60°.

Sides

3

Vertices (corners)

3

Interior angles add up to

180°

Each interior angle (regular)

60°

Each exterior angle (regular)

120°

Diagonals

0

Lines of symmetry (regular)

3

Also called

three-sided figure, three-sided polygon

• The interior angles of any triangle add up to (3 − 2) × 180° = 180°.
• An equilateral triangle has every angle the same, so each one measures 180° ÷ 3 = 60°.
• A triangle has no diagonals — 3 × (3 − 3) ÷ 2.