Mobile Frame Zero: Rapid Attack 001 can be played with most any size of lego model, the common format is to play on what is known as a 7 plate scale. Lego is built on a set of geometric relation between pieces, 3 plates equal a brick in height and so on. By choosing a scale, you help players make frames of similar sized for measuring and gameplay.
In a 7 plate scale, the average human is as tall as 7 lego plates, or two bricks and a plate.
In a 6 plate scale, the average human is as tall as 6 lego plates, or two bricks. This scale is also the size of Lego's microfigures, the same ones seen in most lego board games.