I usually use 1 unit = 1 meter. I've also used 1 unit = 1 character height.

In QuakeIII (and by extension, games based off this engine) the player's bounding box is exactly 56 units tall, with 32 units appearing to be about a meter in game. In the aging game Dark Forces II: Jedi Knight, the player is about .3 units tall, and Kyle Katarn is supposed to be six two. Therefore, I will conclude that the average used in video games is 17.5 units to a meter. This is an average, it is not a bullstat; therefore it must be correct. All games use 17.5 units to a meter.

in unreal editor characters tend to be between 64 and 128 units high.