Types of triangles chart
Triangles are sorted two ways. By their sides they are equilateral, isosceles or scalene; by their angles they are acute, right or obtuse. This chart draws all six, with tick marks on the equal sides and the square that marks a right angle.
Free printable PDF, 3rd grade to 5th grade.
One page, black and white, prints the same every time.
What is on the sheet
By sides
| EquilateralAll three sides equal | IsoscelesTwo sides equal | ScaleneNo sides equal |
By angles
| AcuteAll angles less than 90° | RightOne angle of exactly 90° | ObtuseOne angle more than 90° |
Reading the marks
The short lines across a side are tick marks. Sides with the same number of ticks are the same length, so the equilateral triangle has one tick on every side and the isosceles triangle has one on each of its two equal sides. The scalene triangle's sides carry one, two and three ticks because no two of them match. The small square in a corner marks a right angle.
Every triangle has two names
A triangle gets one name from its sides and one from its angles. The right triangle on this chart is also scalene, and an equilateral triangle is always acute, because each of its angles is 60 degrees. A right triangle can be isosceles, with its two equal sides meeting at the square corner.
Fourth grade sorts triangles by their angles and finds the right triangles (CCSS 4.G.A.2). Fifth grade sorts shapes into families by their properties (5.G.B.4), and the chart is the reference for both.
Common questions
- Is an equilateral triangle also isosceles?
- In most math books today, yes. Isosceles means at least two equal sides, and an equilateral triangle has three. Some older books say exactly two, so check which one your child's class uses.
- Can a triangle be right and obtuse?
- No. The three angles of a triangle add up to 180 degrees, so once one angle is 90 degrees or more, the other two share what is left and both are acute.