Set a map scale by saying how many quants equal a foot (or a meter). In my 3D game, 8 quants make one foot for the outdoor worlds and 32 quants make one inch in the indoor worlds (384 quants make a foot for comparison). So, if a building has 5 floors spaced 12 feet apart, 60 feet tall, you'd have it as 480 quants tall for my 3D game's outdoor worlds (or 23040 quants for the indoor worlds). My 2D game uses a screwier scale, but with a reason for it, but rather than quants, it's coordinate units as I call them. I define a coordinate unit as the distance travelled at 1 mph for a tenth of a second (after one frame in my 2D animations), which is 11/75 of a foot.

For a player 5 feet, 10 inches tall, the typical size for an adult human, you'd have the character 46 2/3 quants tall. It's nothing more than simple multiplication.