Find volume by multiplying
Length × width × height is a formula your child will carry for years: in 6th grade with fractional edges, in 8th grade with cylinders and cones, and in science. Because it is built from layers of cubes, it is a formula your child can rebuild if they forget it. It also answers practical questions, like how much water a 20 by 10 by 12 inch tank holds.
In this video, your child will learn to find volume by multiplying the sides.
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
A box is 4 cm long, 3 cm wide and 2 cm tall. Volume = ? cubic centimeters
Example 2
A shape is made of two boxes. One box is 3 ft long, 2 ft wide and 4 ft tall. The other is 3 ft long, 2 ft wide and 2 ft tall. Volume = ? cubic feet
Your child's turn
A box has a base of 15 square inches. It is 4 in tall. Volume = ? cubic inches
The three key steps
- 1Length × width = base
- 2Then × the height
- 3Volume = length × width × height
Mistakes to listen for
- Adding the three dimensions instead of multiplying, so a 4 by 3 by 2 box gets a volume of 9, not 24.
- Multiplying only two dimensions, finding the area of the base and forgetting to multiply by the height.
- Counting the overlap twice when splitting an L-shaped solid into two boxes, or using the whole shape's length for one part.
The lesson shows every step, so your child sees why it works. Read our parent's guide to finding the volume of a box →
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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 finding the volume of a box, 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 finding the volume of a box 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 →
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Questions at your child's level, about five minutes a day, on finding the volume of a box and whatever PK-5 skills they need to develop. Unlimited practice, free forever.
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