In CC3, you don't really need to "count pixels" because it's a CAD-based program. In an overland map, while no units are listed 10,000 x 8,000 can be in miles or kilometers or whatever unit you desire. In a dungeon, floor plan or city, it can be the same "generic" thing or you can assign a unit like feet or meters.
If you want to scale your symbols, right click the mouse when you are placing them and enter a new value in the "X and Y:" box under Scale. If you want to re-scale the drawing tools that use symbols to draw forests, for example, that's a little more advanced/tricky. I'm not sure of all the steps but you could probably get an answer from one of the Profantasy people at their forums (see link in next paragraph).
If you are brand new to CC3, I recommend checking out the official Profantasy CC3 user forums in addition to The Cartographers Guild to find a lot of help with the basics: http://forum.profantasy.com
Hope this helps.