March 16, 2018
By Caitlin Hardeman

Lesson plan

Calculate Perimeter

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Students will be able to calculate the perimeter of polygons.

(2 minutes)
  • Tell students that you have a problem that you need help solving. Explain that you have this really big yard, and a dog that wants to go out and run around. The only issue is that there is no fence.
  • Ask students to help you determine how much fence is needed in order to enclose the backyard.
  • Allow students to share ideas.
  • Tell them that knowing the perimeter of the yard would help determine the amount of fence needed.
(10 minutes)
  • Explain to students that the PerimeterIs the distance around a two-dimensional shape that has straight lines. It can be calculated by measuring the length of each side and adding them up. The LengthIs how long one side of the shape is.
  • Display the Geometry Basics: Perimeter worksheet so students can see the definition of perimeter and an example of how to CalculatePerimeter, or find the answer.
  • Model thinking aloud about the rest of the problems on the worksheet. (Note: Ignore the word problems from the worksheet for whole group teaching, but these could be used as Enrichment for more advanced learners.)
(15 minutes)
  • Have students find a partner based on the index card they receive. Partners will be formed when a shape with labeled lengths of sides matches with the correct perimeter. Prior to distributing cards, instruct students to determine the type of information (number or shape) they are looking for in the activity.
  • Give each student an index card and offer support for students who may struggle to find their partner.
  • Hand out a copy of the Presenting Perimeter worksheet to each student. They will complete these worksheets in their perimeter partnerships.
  • Go over the worksheet with the class, calling on nonvolunteers to provide answers. Then, call on another student to either agree or disagree, and explain why. Prompt students to use key terms, such as perimeter and length in their explanations.
(10 minutes)
  • Distribute a copy of the Finding the Perimeter worksheet to each student. Point out that there are some shapes where the length is not filled in on all sides. Explain to students that if you know the lengths of other sides that are the same, you can figure out the length of the missing sides.
  • Show an example of how to find the perimeter of a shape with missing lengths.
  • Give students time to complete the independent work, and circulate to assess students’ proficiency levels in calculating perimeter.


  • Intentionally partner students based on academic needs to best support language learners.
  • Create a word wall with geometry terms, including visuals, that students can reference when discussing the perimeter of the different shapes. Include the names and characteristics of shapes and other key terms, such as perimeter, length, sides, and calculate.


  • Provide students with word problems that require them to find the perimeter of a shape, such as the two word problems from the Geometry Basics: Perimeter worksheet.
  • Challenge learners to draw a bird's eye visual of a city. Instruct them to use only polygons, and to include the lengths of all sides. Then, they should calculate the perimeter of each of the city’s structures.
(5 minutes)
  • Give each student an index card for an Exit Ticket.
  • Instruct them to draw a basketball court that has the lengths of 10 feet on the long sides, and 5 feet on the short sides. Direct them to calculate the perimeter of the basketball court.
(3 minutes)
  • Have students brainstorm contexts in which knowing the perimeter of something is beneficial. Possible answers include: construction of a house, fencing off a garden, building a barn, building a swimming pool, planning a marathon around a town.

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