How big of an area can I color with one Copic marker?

With a B4 sized page and a broad nib as reference you would be able to cover around 5 pages with Copic Classic, 3.7 pages with Copic Sketch, 2.7 pages with Copic Ciao and 9 pages with Copic Wide. Please note that it can vary depending of absorption properties of each type of paper so please use these references as directional only.