This depends on the size of the object. If your mesh was 100x100 in Maya at export time, unreal’s 1x1 scaled will be 100x100 cm. I believe the cube that comes predefined is 1 cubic meter. If you need a size reference drag out a BSP brush and set its size to what you want then scale your static mesh accordingly.
I am interested in this as well… When I place BSP cubes in the world they are defaulted to a scale of 1.0 in xyz. This makes it really difficult to follow tutorials as the tutorials show them being scaled and resized in units, not per scale. (For example, if you want a cube to be 250 units high, you type in 250 units, not 25). Is there a way to change the behavior in the 4.19 editor to accommodate this? I do not want to deal with the nightmare of figuring out floats etc to get things to match up correctly by adjust scale as a 1:1