Cardboard Calculator




Introduction: Cardboard Calculator

Known as "Slider Adder Calculator", this system is one of the first mechanical calculators. As their operating principle is simple, it is possible to make one with only some cardboard and some office supplies.

You will learn how to make a calculator allowing you to perform three-digit additions.

If you like the challenge, you can also imagine a version with more digits, or allowing to perform subtractions.


  • Thin cardboard, such as cereal packages

  • Thick cardboard

  • A sheet of checkered paper, or a sheet and a printer

  • Glue (+ adhesive tape but this is optional)

  • A pencil (+ pens / markers for personalization)

  • A ruler

  • Scissors (a cutter may be more convenient for certain steps)

  • A toothpick or anything that can be used as a stylus

Step 1: Preparation of the Strips

Prepare the strips.

Make as many strips as you want figures displayable by the calculator (three in my case).

If you prefer to print them, here is a template in pdf format:

Step 2: Make the Strips Rigid

Cut thick cardboard to the same dimensions as the pieces of paper.

Glue one piece of paper per piece of cardboard.

Step 3: Making the Slides

On thin and smooth cardboard, transfer the sizing of a strip.

U-shaped slides will have to be obtained, so plan the thickness of the additional sliders before cutting and folding.

Check that the strips can slide. If not, adjust them or repeat this step.

Make a slide by strip.

Step 4: Beginning of the Structure

Cut thick cardboard and glue the slides one next to the other.

Allow a margin for the future structure.

Step 5: Continue the Structure and Adjust the Mechanism

Cut three pieces of thick cardboard to circle the slides.

Put the strips in the mechanism.

Adjust the height of the slides by cutting them when they protrude above the strips.

Step 6:

Cut the strips at each line except for the most-right strip.

Also cut the sliders at the lowest right line (visible on the second and third images).

Step 7: Front Panel

Cut a piece of thin cardboard to the same dimensions as your calculator.

Then comes the most delicate step. Report the locations of the various elements on the new piece of cardboard.

Step 8: Almost at the End

Cut out the areas in red on the first image.

Then check that the elements are well aligned like in the third image.

If they are not, try adjusting or repeat the previous step.

Step 9: The End

On the front panel, put the useful annotations (numbers and "R"), then hold it in place. I chose to use adhesive tape but it is possible to stick the edges instead.

Find a pointed object as a stylus, then you're ready to calculate!

Cardboard Speed Challenge

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Cardboard Speed Challenge

2 People Made This Project!


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1 year ago

Do you have a PDF model of the parts?


2 years ago

Oh! So cute! It's a Magic Brain Calculator clone! Very cool!


2 years ago

I've seen this calculator once on a slide rule ( and I also wanted to build it myself but I didn't know exactly how does it work internally. Now I know. Thanx! Great job! I'll build it!
[You have my vote in contest!]


2 years ago

I'm sure you have had many positive responses to this craft/tool project. I would just like to say that it would be more economical if you didn't have such large margins and dead space throughout the PDF file. We are in the middle of the pandemic where schools are closed and students are working from home. With a class size of twenty-three students, only seven are connected to the internet at home. With all the facilities that have internet accessible for my students closed, as well as our district's print shop, I have been making copies from my home computer and then mailing them out. I am on my second XL Black Ink Cartridge and think that even if we weren't in the middle of the COVID-19 Pandemic, it would still be beneficial to spare the paper since most teachers have a very limited supply, as do I. But, all being said, this is a very usable web site and look forward to using many items in my classroom when we return, either this school year or next. As for right now, this Cardboard Calculator is a fun, but useful, project that I'm sure my 6th graders will enjoy.


2 years ago

This is great! Thanks for sharing :)