Regular Decagon (10 sides) — free printable diagram

How many sides does a decagon have?

A decagon is a ten-sided shape — a polygon with 10 sides and 10 corners. A regular decagon has 10 equal sides and 10 equal angles of 144°.

Sides

10

Vertices (corners)

10

Interior angles add up to

1,440°

Each interior angle (regular)

144°

Each exterior angle (regular)

36°

Diagonals

35

Lines of symmetry (regular)

10

Also called

ten-sided figure, ten-sided polygon

• The interior angles of any decagon add up to (10 − 2) × 180° = 1,440°.
• A regular decagon has every angle the same, so each one measures 1,440° ÷ 10 = 144°.
• A decagon has 35 diagonals — 10 × (10 − 3) ÷ 2.