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

If you've ever wondered how many playpen balls it would take to fill up your apartment, but not wanted to do all the calculations yourself, then you are in luck. If you know things like the square feet of your apartment floor, the depth you want to achieve, radius per ball and packing effieciency, then it will tell you how many you need. If you can know how much each ball costs, it will also give you a total price. Fun times.