Fourth Grade Math: Finding the Area of Triangles

This year you will be taking important steps in the process of learning geometry. It's a good idea to learn these concepts well now because you will be seeing them again in high school. Here are some definitions and practice problems to help you out.

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Triangle Geometry

The Area Formula

Area is the amount of two-dimensional space inside the shape. When it comes time to learn how to calculate the area of a triangle, you need to know this formula: A = (1/2)bh. 'B' represents the base of the triangle, which is the line along the bottom of the triangle. 'H' is the height, which is from the center of the base up to the very top of the triangle. You can measure these two lengths with a ruler and then do the calculation on a piece of scrap paper.

Practice Problems

Here's a list of base and height measurements. Using the area formula given above, calculate the area of these shapes. Keep in mind that the abbreviation 'in' stands for inches and 'sq. In.' stands for square inches.

  1. B = 12 in., H = 4 in.
  2. B = 17 in., H = 9 in.
  3. B = 8 in., H = 7 in.
  4. B = 11 in., H = 10 in.
  5. B = 6 in., H = 3 in.


  1. A = 24 sq. in.
  2. A = 76.5 sq. In.
  3. A = 28 sq. In.
  4. A = 55 sq.. In.
  5. A = 9 sq. In.

Types of Triangles

As you may be learning in school, there are several different types of triangles. Three that you will probably be seeing in your textbook are called acute, obtuse, and right. Acute triangles get their name from acute angles, which are less than 90 degrees. So to have an acute triangle, all three angles must measure less than 90 degrees.

An obtuse triangle is where at least one angle measures more than 90 degrees. Can you guess what a right triangle is? A right triangle has at least one angle measuring exactly 90 degrees. Usually three angles of a triangle must total 180 degrees, regardless of whether the angles are obtuse, acute or right.

More Triangle Vocabulary

Isosceles Triangles
These occur when you have two sides of a triangle measuring the same length and the same angles.
Equilateral Triangles
These are when each of the three lengths are the same and each of the angles are also the same.
Scalene Triangles
Sometimes a scalene triangle is also a right triangle, but not always. These occur when the three sides are the same length but none of the angles are the same.
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