The average height for outlets is 12 inches from the floor to the center of the outlet box.
Outlet height from floor code.
For convenience outlets such as those fitted in the kitchen you will find that these are around 42 inches in height or over the surface of your work tops.
Standard height for outlet boxes.
Some states such as california require this minimum height.
Electrical receptacle outlets on branch circuits of 30 amperes or less and communication system receptacles shall be located no more than 48 inches 1219 mm measured from the top of the receptacle outlet box nor less than 15 inches 381 mm measured from the bottom of the receptacle outlet box to the level of the finished floor or working platform.
Recreational outlets for tvs or computers will usually be no more than 12 inches off of the floor and may be considerably less.
When upgrading home electrical wiring or remodeling the actual height can be adjusted so the elevations of the switches and outlets will match other existing outlets and switches.
Height above the floor the nec has no official requirement concerning the height of a receptacle above any finished floor including the kitchen floor.
Remodeling and upgrading home electrical wiring.
The standard height for wall outlet boxes is about 12 inches from the top of the floor covering to the bottom of the receptacle box or 16 inches to the top of the box.
If you are setting box heights prior to the installation of the subfloor floor covering or any underlayment be sure to account for this expected height difference.