1 A retired Regular officer who also is employed by the federal government and is subject to the dual compensation statutes may have that reduction reduced because of the waiver of retired pay to receive VA benefits.
If they don't, then 4 thick is usually standard for a patio slab, how large or small it is doesn't really matter. The most important part is the sub-base. Make sure you have a good gravel base. I would recommend at least 12 inches of compacted gravel. I like gravel where the aggregate (rocks) are no larger than 1.
1 Excavate the slab area to a depth of about 7 inches, allowing 3 inches for a gravel base and 4 inches for concrete.  Check the forms for level (Â¼ inch for every 12 feet is sufficient to allow for rain run-off). Patio and sidewalk forms should slope evenly away from structures.