DPI calculator for print

I recently had to print a large format canvas, and I noticed the printing company understood inches and DPI (dots-per-inch) but it did not understand megapixels. They told me: your 4000 x 4000px image is too small, but they could not tell me how big it had to be.

So I made a calculator for it: if you want to print a canvas of 60x60cm (23.6×23.6 inch) at 300 dpi with a bleed of 2mm, you need a 7134 px x 7134 px image (+- 51 megapixel)
http://toolstud.io/photo/dpi.php

Given the fact that most digital cameras do not have that resolution, this probably means you will have to ‘upsize’ your source image. For some background on that, read http://blog.forret.com/2006/08/23/how-to-upsize-an-image/