Here is a fun LEGO® math activity – build a balance out of LEGO® bricks and find objects to weigh!

Gresham (3rd grade), Owen (K), and I really enjoyed this LEGO® math project. When I told them what we were doing, they didn’t quite get it. But when the saw what the balance could do, they said, “Oh, that’s really cool!”

Build a LEGO Balance - Math Activity for Kids

Here is the design that we used for the balance:

Build a LEGO Balance - Math Activity for Kids

It’s super simple – these connector pieces allow the arms of the balance to rotate freely.

Build a LEGO Balance - Math Activity

As long as you build the baskets for the balance exactly the same, and center your connector pieces, your balance should sit evenly.

The boys were eating goldfish while we were building this, so we ended up using those as weights – ha! Gresham decided to find out how many goldfish his toy alligator was equal to. We were all surprised that the tiny alligator was equal to 8 goldfish!

Build a LEGO Balance - Math Activity for Kids

Then we compared a toy car with goldfish. Uh, we quickly decided that we needed a different comparison weight!

Build a LEGO Balance

So we tried pennies.

Build a LEGO Balance - Math Activity for Kids

Gresham made a chart of our findings.

Build a LEGO Scale

We also tried comparing objects with how many LEGO® bricks they weigh. Other ideas – compare items with paper clips, raisins, small stones.

This project was a lot of fun! We’ve been slogging through school lately, trying to endure to the end of the year, so it was nice to find something to make math a little more interesting.

Be sure to stop by the rest of the LEGO week posts!

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  1. Faye May 8, 2015

    This is very cool and creative! I have a million Legos stored from when my kids built with them (They are now 25, 24, 23). I have a home daycare and let my schoolagers build with them if I have any enrolled, but keep them out of the way of the little ones; they have the larger ones and Duplos. We are going to try this! Thanks for sharing!!

  2. Lisa K May 10, 2015

    We did this and loved it! Thanks so much for your great work. Blessings!

    1. Leanne Nov 30, 2016

      what set(s) did you have?

  3. There's Just One Mommy May 28, 2015

    Don't you just love all you can do with Legos!?
    What a fun idea!

    We need to get that piece in the middle so we can try this one day. Love it!

  4. Joy Feb 27, 2016

    Good afternoon,

    I'd love to do this for my STEAM Club at the library. For the connector piece, is it the Axle Pin?

    Is this the piece ---

    Thank you,

    1. Sarah Feb 27, 2016

      No, those are not the right ones. I just went up and tested one of those with our Legos, and the side with ridges won't click in to the Lego Technic bricks. Look on for a Technic pin, without friction ridges. Here's a link: I really like Brick Link for ordering individual pieces. Good luck with your STEM club! Sounds fun!

      1. Erin Mar 17, 2018

        Do you have a link for the long pieces with holes?

  5. JustCorey Mar 22, 2018

    My 2nd grader used this design at cub scouts for their Adventure in Coins activities. All the other Wolves in his den enjoyed taking turns using it to weigh coins against other items. Thanks

  6. Heather Jan 19, 2019

    Where did you find the connector pieces to make this?

  7. Geneviève Vigneault May 15, 2020

    so cool, my son love it!!!

  8. Kristen Jun 29, 2020

    My five year old loved making this! Thanks for the idea

  9. Eve Webb May 29, 2022

    Looking through for some ideas for long winter rainy days. It's still fairly warm, so not too bad. This one will be great for all the older grandchildren, aged 4,5,8,10 as they can work together to hunt up pieces and build then find things to weigh. Wish those goldfish were available here, my oldest daughters remember them from living in the US.Thankyou for your many ideas.


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