Go to a image size checking website to get its dimensions, look at the artwork and count how many pixels wide the drawing is (if its pixel art) then you can determine the scaling. for instance if the drawing is 13 pixels wide, but the image size thingy tells you its 65 pixels wide, that means each pixel is 65/13 = 5 pixels wide. So you go to another scaling website and scale it by two to get 10 pixel scaled pixels.