Area of Triangles and More


Our Area of Triangles and More lesson plan teaches students how to find the area of triangles and other shapes such as trapezoids and parallelograms. Students practice using the formula to find the area for each of these shapes and more.

Included with this lesson are some adjustments or additions that you can make if you’d like, found in the “Options for Lesson” section of the Classroom Procedure page. One of the optional additions to this lesson is to have students find examples of polygons in the classroom or around the school.

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What our Area of Triangles and More lesson plan includes

Area of Triangles and More equips students to identify and use the formula for the area of triangles, trapezoids, and parallelograms such as the rhombus and other quadrilaterals. This lesson also briefly reviews the application of the commutative property of multiplication in these formulas. This lesson is for students in 5th grade and 6th grade.

Classroom Procedure

Every lesson plan provides you with a classroom procedure page that outlines a step-by-step guide to follow. You do not have to follow the guide exactly. The guide helps you organize the lesson and details when to hand out worksheets. It also lists information in the blue box that you might find useful. You will find the lesson objectives, state standards, and number of class sessions the lesson should take to complete in this area. In addition, it describes the supplies you will need as well as what and how you need to prepare beforehand. The supplies you will need for this lesson are straws, scissors, rulers, scratch paper, calculators, and the handouts. To prepare for this lesson ahead of time, you can gather the supplies, pair students for the activity, and copy the handouts.

Options for Lesson

Included with this lesson is an “Options for Lesson” section that lists a number of suggestions for activities to add to the lesson or substitutions for the ones already in the lesson. An optional addition to the lesson activity is to glue the finished polygons to colored construction paper and label all of the measurements for each. You can also have students use either toothpicks or craft sticks to create the polygons for the activity, instead of straws. Another optional addition to the lesson is to have students find examples of polygons in the classroom or around the school. You could also have students make a hanging mobile of polygons. If you’d like, you can use either the practice or homework page as a quiz or test. Finally, to close the lesson, you can have students complete an art activity where they use different polygons to create an artistic design.

Teacher Notes

The teacher notes page includes a paragraph with additional guidelines and things to think about as you begin to plan your lesson. This page also includes lines that you can use to add your own notes as you’re preparing for this lesson.


The Triangle

The Area of Triangles and More lesson plan includes two pages of content. The lesson begins by stating that a triangle is basically just half (1/2) of a square or rectangle. Before learning how to find the area of a triangle, it’s a good idea to review how to find the area of a rectangle and square. The basic formula is length times width. Since all of the sides of a square are the same length, the formula for finding the area of a square is to simply square the length of the side.

Triangles are half of a four-sided figure. This means that its area is also half of its size. When you split a rectangle into two triangles, they will have the same measurements. For a rectangle with a total area of 48 square units, the area of each triangle is 24 square units. However, most triangles will not be part of a rectangle; they will be on their own.

When measuring a triangle, the two measurements are called the base and the height. For example, triangle B (shown in the lesson) has a base that’s 8 units long and a height that’s 6 units high. To find the area, you multiple base times height (for 48 square units). Next, you take half of that amount to find the area. Half of 48 is 24, so the area of this triangle is 24 square units. The lesson then includes several other examples, with diagrams.

The base of a triangle is kind of like the length of a rectangle, and the height is kind of like the width. You just have to multiply them together and then halve it to find the area. Being able to find the area of a triangle will help you find the area of other kinds of shapes, like trapezoids, parallelograms, rhombuses, and irregular quadrilaterals.

Other Polygons and Area

To find the area of these other polygons, you can divide them into multiple triangles, find the area of each, and then add them together. However, there’s an easier way to find the areas of these shapes, as they all have their own area formulas! The lesson includes a very helpful chart that lists each type of polygon, its formula for area, and an example for each.

While these formulas may seem complicated, all you have to do is replace each variable with the correct value or measurement. Three of the four formulas include the fraction 1/2. It’s important to make sure to pay attention when solving for the area of a polygon. The good news is that if you forget one of these formulas, you can divide the polygon up into triangles and use the formula to find the area of a triangle!


The Area of Triangles and More lesson plan includes three worksheets: an activity worksheet, a practice worksheet, and a homework assignment. You can refer to the guide on the classroom procedure page to determine when to hand out each worksheet.


Students will work with a partner to complete the activity worksheet. They will use straws to show “diagonals” and will use them to create 10 examples of polygons. They should cut the straws or join them together as needed to create the right lengths. Each pair will then sketch each polygon, including measurements in inches or centimeters. They should include the measurements for the base, height, and any other necessary values. Next, they will use the formulas provided in this lesson to find the area and perimeter of each polygon. They should also use the diagonals to create triangles within each polygon.

They will finish the activity by answering five questions. These questions ask them to sketch various shapes, like triangles, trapezoids, and a rhombus, and answer questions about them. They also must answer a question about using diagonals and a question that asks which polygon’s area and perimeter was hardest to determine.

Students can work alone for this activity if you’d prefer.


For the practice worksheet, students will complete two exercises. For the first, they will read word problems and find the area using the given measurements, showing the formulas they use and their work. And for the second, they will find the area of each figure shown on the worksheet.


The homework assignment asks students to complete three exercises. The first asks them to match the area formula with its polygon. The second asks them to answer questions about the lesson material. Finally, the third asks them to find the area asked for in short word problems.

Worksheet Answer Keys

This lesson plan includes answer keys for the activity worksheet, the practice worksheet, and the homework assignment. If you choose to administer the lesson pages to your students via PDF, you will need to save a new file that omits these pages. Otherwise, you can simply print out the applicable pages and keep these as reference for yourself when grading assignments.

Additional information


5th Grade, 6th Grade



State Educational Standards


Lessons are aligned to meet the education objectives and goals of most states. For more information on your state objectives, contact your local Board of Education or Department of Education in your state.