What a want to do is a big cylinder which is going to have a diameter of .285 m and do several cut loops but when I want to do an scale and type the units of that cut loop (for example 0.335 m) in meters it gives me an smaller circle instead of a bigger one and that's incorrect due to the units of the original cylinder.
As mentioned, Scale is unitless, it's just a multiplier for the actual Dimensions.
The only solution is to divide the Final Dimension by the Current Dimension (FD/CD). You can type that directly into the scale value, Blender calculates it for you. So in your case type
.335 / .285 which will result in a Scale of
1,17544 and your loop will have the correct dimension.
When doing a lot of dimensioned work, can be useful to have a collection of home-made measures around to use as snap targets.
So for example, in this case, I've CtrlR cut a loop into the cylinder, and P separated the selection into a new object. Then you can set its dimensions in the 'Dimensions' section of the Transform panel in the 3D View CtrlA > Apply the scale after doing this.. of course, you can give the object a useful name.
With snap set to 'Vertex' and 'Active' and snaps set to influence all transforms, SShiftZ scaling other loops in XY, can be snapped to the measure.
Once a few dimensions have been set this way, nearly all others can be taken from existing parts, temporarily duplicating bits to snap to.