Find the perimeter
Fences, picture frames, and bulletin-board borders all give your child a reason to think about perimeter, the distance around an edge. Comparing it with area helps your child keep the two measurements separate, which matters in 4th grade when they use both to solve real problems. Working out a missing side also builds the backward reasoning that algebra relies on later.
In this video, your child will learn to find the perimeter of a shape.
The lesson stops at each question for your child's answer.
Three problems, each a little harder
Each problem is worked step by step. Your child will solve the last one before Bobby shows how.
Example 1
5 cm long, 3 cm wide. Perimeter = ? cm
Example 2
Perimeter = 24 cm, length = 8 cm. Width = ? cm
Your child's turn
Perimeter = 20 m, length = 7 m. Width = ? m
The three key steps
- 1Perimeter: the distance around.
- 2Add all the sides.
- 3Missing width? Take away, halve.
Mistakes to listen for
- Adding only the two side lengths shown, so a 5 by 3 rectangle gets a perimeter of 8 instead of 16.
- Multiplying the sides to find perimeter, mixing it up with area, so a 5 by 3 rectangle gets 15.
- Assuming equal perimeters mean equal areas, so a 7 by 1 rectangle and a 4 by 4 square seem the same size.
The lesson shows every step, so your child sees why it works. Read our parent's guide to perimeter: the distance around a shape →
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Questions parents ask
Does my child need an account to watch?
No. You can watch this on any device at any time. If your child would like to practice perimeter: the distance around a shape, and you'd like parent-friendly reports on your child's progress and growth, you can join Bobby's Math Club for unlimited free practice.
What happens when my child answers a question?
A right answer gets a cheer, and the lesson carries on. If your child isn't sure, they can tap "I don't know yet", and Bobby gives the answer and shows another example. Nothing is scored or stored.
Is this the same lesson that's on YouTube?
Yes. Here, the lesson stops at each question and waits for your child to answer. On YouTube, each question stays on screen for a few seconds, and then the lesson plays on.
Where can I learn more?
There's a short, kid-friendly lesson like this one for every Pre-K to 5th grade math skill, all in our video library. Our parent's guide to perimeter: the distance around a shape has more on where kids get stuck and how you can help at home. In the club, your child practices at just the right level, about five minutes a day, and you get parent-friendly reports as they grow. Learn more about how it works →
Practice perimeter: the distance around a shape
Questions at your child's level, about five minutes a day, on perimeter: the distance around a shape and whatever PK-5 skills they need to develop. Unlimited practice, free forever.
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