How to set sprites Pixel Per Unit ?

Hi guys, I often read that for using 2D physics, pixel per unit for sprites must be 1 unit per meter.

Does that mean that for a big sprite, 2048x2048px for a real size of 72x72cm I have to set my pixel per unit at... (100cm x 2048px)/72cm = 2800 ?!

That seems pretty huge compares to the values people usually work with, isn"t it ? Well, my sprites are big, that's a fact, but even if I go for 1024px, it's still waaaay bigger than the usual 100pixel per unit (or worst, the 1pixel per unit, like some people advice).