Inspired by the following xkcd:
Click to go back to this original comic on xkcd.

How many playpen balls would it take to fill your apartment?

The suggestions given below are just that--feel free to enter nonsensical values for fun and profit.

Packing efficiency: %
The theoretical best possible packing density is about 74%, and the theoretical worst (in a space whose dimensions are multiples of a ball's diameter) is about 60% before you stop actually filling the space or start ignoring gravity. Don't believe me? Figure it out yourself.

I recommend excluding bathrooms for sanitary reasons.

If you don't have screen windows, you probably want to stay under sill level … or get screen windows.

Floor area to cover: ft.²
Depth of balls: ft.
Radius of each ball: in.
Price of each ball: $

It would take balls and cost dollars to fill your apartment with playpen balls.

Frequently Asked Questions

  • Are you sure this is right? It says I need many fewer balls than I expected.

    You might be putting the diameter in the radius field. The radius is half the diameter, so if you're looking at 3" diameter balls, put 1.5 where it asks for radius.

  • Is there a metric version?

    Yes! Berge made it, and it's here.

  • What if I want to factor in the cost of building a PVC frame for my ball pit?

    Jeff has you covered.

  • Do you know where I can buy some playpen balls?

    No, I don't. Sorry! If you find a supplier you like, let me know and I'll put a link here. Dillon liked the speed and quality of Feel free to send more suggestions!

  • Will you sell me some playpen balls?

    Nope, I don't have any. See above, though.

  • Can I ask you more questions/send you pictures of the ball pit I made with this calculator/buy you a beer?

    Sure! Shoot me an email: