What's the standard height for an outlet?
The direct answer to your question is "There is no standard". Outlets can be installed at whatever height is comfortable for the intended use.  The only NEC requirement is that you must be within 6 feet of an outlet along any wall (12' between outlets, A unbroken wall space of 2 feet or more including space measured around a corner requires an outlet. ref. NEC 210.52.A.2. A common height for a wall outlet is between 12 to 16 inches to the bottom of the device. In rare instances, outlets are still installed in baseboards and in the floor with proper box/covers.