Equilateral Triangle — free printable diagram

What is an equilateral triangle?

An equilateral triangle has three sides of equal length and three equal angles. Because the angles in any triangle add up to 180°, each angle in an equilateral triangle must be 180° ÷ 3 = 60°.

Sides

3

Equal sides

All 3

Equal angles

All 3, each 60°

Angles add up to

180°

Lines of symmetry

3

Rotational symmetry

Order 3

• Equal sides and equal angles come as a pair: if all three sides match then all three angles must too, and the other way round.
• Under the usual definition of isosceles — “at least two equal sides” — every equilateral triangle is also isosceles, since having three satisfies it. Some primary schemes teach isosceles as “exactly two”, which excludes it, so check which your syllabus uses.
• It is the only triangle whose angles are fixed. Any equilateral triangle, at any size, has three 60° angles — which is why they tessellate, six meeting at a point to make 360°.
• Three lines of symmetry, one through each vertex to the midpoint of the opposite side, and rotational symmetry of order 3.