What app can calculate sticker quantities based on print area?

[thesafetysign]

Hi All

I'm have a printing  / safety sign printing website.

I want to add vinyl stickers to my site now for contractors etc. I sell these by a certain print area of vinyl. Im on the lookout for an app or something where the user can input their size of sticker and it will calculate how many stickers they will get per certain print area. 

I have tried searching with no avail. Maybe I'm looking for the wrong thing I am not too sure. Any help would be greatly appreciated.

Thanks in advance.