Grade 3 · Measurement & Data · MAT-03-MD-012
Find Perimeter of Polygons
Represent find perimeter of polygons with words, symbols, diagrams, or models appropriate to Grade 3.
Learning objectives
What you should be able to do
- Represent find perimeter of polygons with words, symbols, diagrams, or models appropriate to Grade 3.
- Solve problems involving find perimeter of polygons accurately and explain why the method works.
- Check results for reasonableness using a second representation, inverse relationship, benchmark, or property when appropriate.
Prerequisite check
Make sure the foundation is ready.
Checks conceptual readiness before new Grade 3 reasoning.
Checks whether prior skills are available for use, not only recalled by name.
Learn
Build the idea from meaning, not memorization.
Meaning of Find Perimeter of Polygons
Perimeter is the total distance around a polygon's boundary.
A reliable reasoning strategy
Add every side length once; when sides are equal, multiplication can replace repeated addition.
Representations that should agree
Perimeter measures boundary length, which is different from the surface area inside. A correct model, equation, verbal explanation, or diagram should preserve the same quantities and relationships.
How to check the result
Check whether the answer fits the quantities, units, and structure of the problem. Use a second representation or inverse relationship when available, and explain what would make an answer unreasonable.
Interactive math lab
Change it. See what stays true.
Geometry Explorer
- build a model
- change one quantity
- predict before calculating
- explain why the result changes
Worked examples
Twenty different ways to see the concept work.
A rectangle is 4 units long and 4 units wide. What is its perimeter?
2 × 4 = 8; 2 × 4 = 8; 8 + 8 = 16Add every side length around the boundary once.
A rectangle is 5 units long and 6 units wide. What is its perimeter?
2 × 5 = 10; 2 × 6 = 12; 10 + 12 = 22Add every side length around the boundary once.
A rectangle is 6 units long and 2 units wide. What is its perimeter?
2 × 6 = 12; 2 × 2 = 4; 12 + 4 = 16Add every side length around the boundary once.
A rectangle is 7 units long and 4 units wide. What is its perimeter?
2 × 7 = 14; 2 × 4 = 8; 14 + 8 = 22Add every side length around the boundary once.
A rectangle is 8 units long and 6 units wide. What is its perimeter?
2 × 8 = 16; 2 × 6 = 12; 16 + 12 = 28Add every side length around the boundary once.
A rectangle is 9 units long and 2 units wide. What is its perimeter?
2 × 9 = 18; 2 × 2 = 4; 18 + 4 = 22Add every side length around the boundary once.
A rectangle is 10 units long and 4 units wide. What is its perimeter?
2 × 10 = 20; 2 × 4 = 8; 20 + 8 = 28Add every side length around the boundary once.
A rectangle is 3 units long and 6 units wide. What is its perimeter?
2 × 3 = 6; 2 × 6 = 12; 6 + 12 = 18Add every side length around the boundary once.
A rectangle is 4 units long and 2 units wide. What is its perimeter?
2 × 4 = 8; 2 × 2 = 4; 8 + 4 = 12Add every side length around the boundary once.
A rectangle is 5 units long and 4 units wide. What is its perimeter?
2 × 5 = 10; 2 × 4 = 8; 10 + 8 = 18Add every side length around the boundary once.
A rectangle is 6 units long and 6 units wide. What is its perimeter?
2 × 6 = 12; 2 × 6 = 12; 12 + 12 = 24Add every side length around the boundary once.
A rectangle is 7 units long and 2 units wide. What is its perimeter?
2 × 7 = 14; 2 × 2 = 4; 14 + 4 = 18Add every side length around the boundary once.
A rectangle is 8 units long and 4 units wide. What is its perimeter?
2 × 8 = 16; 2 × 4 = 8; 16 + 8 = 24Add every side length around the boundary once.
A rectangle is 9 units long and 6 units wide. What is its perimeter?
2 × 9 = 18; 2 × 6 = 12; 18 + 12 = 30Add every side length around the boundary once.
A rectangle is 10 units long and 2 units wide. What is its perimeter?
2 × 10 = 20; 2 × 2 = 4; 20 + 4 = 24Add every side length around the boundary once.
A rectangle is 3 units long and 4 units wide. What is its perimeter?
2 × 3 = 6; 2 × 4 = 8; 6 + 8 = 14Add every side length around the boundary once.
A rectangle is 4 units long and 6 units wide. What is its perimeter?
2 × 4 = 8; 2 × 6 = 12; 8 + 12 = 20Add every side length around the boundary once.
A rectangle is 5 units long and 2 units wide. What is its perimeter?
2 × 5 = 10; 2 × 2 = 4; 10 + 4 = 14Add every side length around the boundary once.
A rectangle is 6 units long and 4 units wide. What is its perimeter?
2 × 6 = 12; 2 × 4 = 8; 12 + 8 = 20Add every side length around the boundary once.
A rectangle is 7 units long and 6 units wide. What is its perimeter?
2 × 7 = 14; 2 × 6 = 12; 14 + 12 = 26Add every side length around the boundary once.
Practice
Guided practice with hints
01A rectangle is 10 units long and 4 units wide. What is its perimeter?
Hint: Add every side length once; when sides are equal, multiplication can replace repeated addition.
Answer: 28 units
02A rectangle is 3 units long and 6 units wide. What is its perimeter?
Hint: Add every side length once; when sides are equal, multiplication can replace repeated addition.
Answer: 18 units
03A rectangle is 4 units long and 2 units wide. What is its perimeter?
Hint: Add every side length once; when sides are equal, multiplication can replace repeated addition.
Answer: 12 units
04A rectangle is 5 units long and 4 units wide. What is its perimeter?
Hint: Add every side length once; when sides are equal, multiplication can replace repeated addition.
Answer: 18 units
05A rectangle is 6 units long and 6 units wide. What is its perimeter?
Hint: Add every side length once; when sides are equal, multiplication can replace repeated addition.
Answer: 24 units
06A rectangle is 7 units long and 2 units wide. What is its perimeter?
Hint: Add every side length once; when sides are equal, multiplication can replace repeated addition.
Answer: 18 units
Practice
Independent practice
01A rectangle is 6 units long and 2 units wide. What is its perimeter?
Answer: 16 units
02A rectangle is 7 units long and 4 units wide. What is its perimeter?
Answer: 22 units
03A rectangle is 8 units long and 6 units wide. What is its perimeter?
Answer: 28 units
04A rectangle is 9 units long and 2 units wide. What is its perimeter?
Answer: 22 units
05A rectangle is 10 units long and 4 units wide. What is its perimeter?
Answer: 28 units
06A rectangle is 3 units long and 6 units wide. What is its perimeter?
Answer: 18 units
07A rectangle is 4 units long and 2 units wide. What is its perimeter?
Answer: 12 units
08A rectangle is 5 units long and 4 units wide. What is its perimeter?
Answer: 18 units
Common mistakes
Learn to catch the error, not just the answer.
Trace the entire boundary and account for every side exactly once.
Reconnect the answer to find perimeter of polygons and verify that the model, calculation, and label describe the same quantity.
Applications & challenge
Use the idea beyond a single exercise.
Applications
- Find fencing, borders, frames, and walking distances around shapes.
- Use find perimeter of polygons to interpret or solve a Grade 3 situation with quantities, diagrams, measurements, or data.
Challenge problems
A rectangle is 10 units long and 6 units wide. What is its perimeter?
32 units
A rectangle is 3 units long and 2 units wide. What is its perimeter?
10 units
A rectangle is 4 units long and 4 units wide. What is its perimeter?
16 units
A rectangle is 5 units long and 6 units wide. What is its perimeter?
22 units
Flashcards
Retrieve it from memory.
Flashcards
Card 1 of 4
Game mode
Find Perimeter of Polygons Challenge
Solve and explain Grade 3 problems involving find perimeter of polygons without relying on answer guessing.
Practice
Mastery check
01A rectangle is 6 units long and 4 units wide. What is its perimeter?
Answer: 20 units
02A rectangle is 7 units long and 6 units wide. What is its perimeter?
Answer: 26 units
03A rectangle is 8 units long and 2 units wide. What is its perimeter?
Answer: 20 units
04A rectangle is 9 units long and 4 units wide. What is its perimeter?
Answer: 26 units
05A rectangle is 10 units long and 6 units wide. What is its perimeter?
Answer: 32 units
06A rectangle is 3 units long and 2 units wide. What is its perimeter?
Answer: 10 units
07A rectangle is 4 units long and 4 units wide. What is its perimeter?
Answer: 16 units
08A rectangle is 5 units long and 6 units wide. What is its perimeter?
Answer: 22 units
Terminology
Words to know
- perimeter
- The total length around a closed figure.
- polygon
- A closed two-dimensional figure made of straight segments.
Continue learning
Connected concepts
Curriculum references
Standards and instructional references
California Common Core State Standards for Mathematics — Grade 3, 3.MD.8
Primary standards alignment for Find Perimeter of Polygons.2023 Mathematics Framework for California Public Schools
Instructional emphasis on reasoning, representations, problem solving, and equitable access.