Here is a fun LEGO® math activity – build a balance out of LEGO® bricks and compare the weights of different objects.

This math activity works well for kids in the early elementary grades. I’d recommend it for kindergarten up through third grade. Kindergartners will enjoy exploring this LEGO balance, while older kids can really understand the concept of both sides being equal.

In fact, you really can tie this LEGO balance to pre-algebra skills. When the scale is balanced, you know that the contents of both sides are equal. You can imagine an equal sign between them. If you add weight to one side, you’ll need to add the same amount of weight to the other side! So this might be a great hands-on activity for middle schoolers.

This post was originally published in May 2015 and updated in February 2024.

Kids should be able to build this LEGO balance with the bricks they have. These are definitely common pieces!

Your LEGO balance will be able to rotate freely, allowing you to find the weight that will balance it exactly.

Did you know that one large marble is equal to four small ones?

I guess this will depend on the brand of marbles you have, however!

How to Build a LEGO Balance

Gather the pieces shown below. We used two 1 x 16 Technic bricks, a 2 x 2 brick with two pins, and two 2 x 4 plates.

If you don’t have the brick with two pins, another option is to use light gray Technic pins. You’ll need a couple of 1 x 4 Technic bricks to put in the center between the two longer Technic bricks.

If you don’t have 1 x 16 Technic bricks, you can use shorter ones. Create the full length by using plates to attach regular bricks to the Technic bricks that you do have. You’ll want your balance to be at least 16 studs wide or it won’t balance very well.

Insert the pins on the 2 x 2 brick into the center hole on each 1 x 16 Technic brick. Then add 2 x 4 plates on the ends for stability.

Now build a stand for your balance. Ours is just a stack of 2 x 4 bricks!

Build two baskets to hold the objects that you want to weigh. Make sure that the baskets are exactly the same. We used two 4 x 6 plates for the base of each basket.

Using smaller bricks but more of them actually involves more plastic, and the mass of that basket would be a little more, so try to use the same bricks on both.

Attach your baskets to the balance, and you’re ready to go!

How does a balance scale work?

Your LEGO balance won’t tell you how much something weighs in grams or pounds, but it will allow you to compare objects. If you want to find a weight in grams, you can try comparing an object on one side of the scale with paper clips on the other side. Each paper clip will weigh about 1 gram.

Math Activity: How many pennies does it weigh?

We decided to choose objects from around the house to compare with pennies.

Start by putting the object you want to weigh on one side of the balance. Then add pennies one at a time until the scale is balanced.

We made a simple chart to record our results.

A large marble weighed 8 pennies, while a Hot Wheels car weighed 11 pennies!

Ideas for Items to Weigh:

  • Eraser
  • Small rock
  • Toy car
  • Small toy animal
  • Toy figurine
  • Pencil sharpener
  • Keychain
  • Anything you can fit in the LEGO basket!

This project is part of our LEGO STEM book, Genius LEGO Inventions with Bricks You Already Have. Build this plus 39 more machines and gadgets with the bricks you already have! Most of the projects in the book are not on my website.

Want more LEGO STEM activities?

Here’s a collection of 10+ LEGO STEM Projects that everyone should try! Construct a pulley system, spinning tops, a rubber band powered car, and more.

LEGO® is a trademark of the LEGO® group of companies which does not sponsor. authorize, or endorse this site.


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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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