What are the 6 types of triangles?

By sides: equilateral, isosceles and scalene. By angles: acute, right and obtuse. Every triangle has one name from each list, like right isosceles or acute scalene.

What grade is this types of triangles worksheet for?

It is written for grades 3–5 and matches Common Core standards 4.G.A.2, 5.G.B.3, 5.G.B.4.

Is there an answer key for this types of triangles worksheet?

Yes. The last page of the PDF has every answer, so you can mark the sheet in a few minutes and talk through any mistakes together.

Classifying triangles worksheet

Forty questions on classifying triangles: name each triangle by its sides and by its angles, give both names, decide whether a triangle is possible, and find missing sides.

Download the free types of triangles worksheet (PDF)

Types of triangles worksheet

PDF · US Letter · Grades 3–5 · 40 questions · answer key included

Download the PDF

What’s on the worksheet

40 questions on types of triangles, sized for US Letter paper
2 pages of questions plus an answer key on the last page
Written for grades 3–5, matching Common Core 4.G.A.2, 5.G.B.3, 5.G.B.4
Name and date lines at the top, and room to show the work

Sample questions from this worksheet

Name the triangle by its sides (sides 7 cm, 7 cm, 4 cm).
Name the triangle by its angles (90°, 50°, 40°).
Angles 20°, 30° and 130°: acute, right or obtuse?
Give both names: angles 90°, 45°, 45°.
Can it be a triangle? Sides 2 cm, 3 cm and 8 cm.
An equilateral triangle has a perimeter of 27 cm. How long is each side?

Preview the worksheet and answer key

Practice types of triangles online

Between worksheets, a few minutes of online practice keeps the skill fresh. The triangles practice shows a triangle with its sides or angles marked and asks for its name, with the working shown after a wrong answer. The types of triangles lesson has a quiz too.

Types of triangles: a worked example (A triangle with angles 90°, 45° and 45°)

Look at the angles: one is 90°, so by angles it is a right triangle.
Two angles are equal (45° and 45°), so two sides are equal too.
Two equal sides make it isosceles.
Both names together: a right isosceles triangle.

How to use it at home and in class

At home

Have your child sort triangles twice: once by sides with a ruler, once by angles with the corner of a sheet of paper. Part D joins the two names, which is where the understanding shows. For Part E, try making triangles from straws cut to the given lengths. The types of triangles lesson has pictures of every kind. Ten problems a day works better than a whole sheet at once. Mark them together with the answer key, then ask your child to explain one they got wrong: finding the mistake themselves is where the learning happens.

In class

Use the first row as a warm-up, a full page for independent practice, or five questions as an exit ticket. For a retake or a second group, make a new version with the test maker so every child gets different numbers.

Mistakes to watch for

Mixing up the two ways: calling a triangle “right scalene isosceles”.
Calling a triangle acute because one angle is small, even though another is over 90°.
Thinking any three lengths make a triangle. 2 cm, 3 cm and 8 cm can’t meet.
Forgetting that an equilateral triangle is always acute.

What to practice before and after types of triangles

Before: quadrilaterals. If this sheet is a struggle, go back a step.
After: perimeter, once this one is mostly right.
Learn it first: the types of triangles lesson.