Blender does not, I think, have any set scale, you are just supposed to work with proportions. FG treats one blender 'unit' at 1 meter, but it's difficult to tell just using the grid in Blender, especially as many FG things are much bigger than the grid's default size.
One way you can do it is to make a scale object, so add a cube, hit S to scale and then type in the size you want in meters. You can then align things by eye to the cube. I also tend to fine-scale stuff in a similar way at the very end of the modelling process.