Regular Octagon (8 sides) — free printable diagram

How many sides does an octagon have?

An octagon is an eight-sided shape — a polygon with 8 sides and 8 corners. A regular octagon has 8 equal sides and 8 equal angles of 135°.

Sides

8

Vertices (corners)

8

Interior angles add up to

1,080°

Each interior angle (regular)

135°

Each exterior angle (regular)

45°

Diagonals

20

Lines of symmetry (regular)

8

Also called

eight-sided figure, eight-sided polygon

• The interior angles of any octagon add up to (8 − 2) × 180° = 1,080°.
• A regular octagon has every angle the same, so each one measures 1,080° ÷ 8 = 135°.
• An octagon has 20 diagonals — 8 × (8 − 3) ÷ 2.