Also, 12 gage wire is rated to carry 20 amps and is commonly used on 120 volt outlet circuits. 14 gage wire is rated at 15 amps and is commonly used for lighting circuits on 120 volt systems.

To expand on Phil's answer. Generally outlets are part of a lighting circuit protected by a 15 amp breaker, sou there are outlets feed with14 gauge wire. In the US mode codes require that a kitchen have a minimum of two 20 amp outlet circuits, as Phil indicated they would be feed by 20 gauge wire. Circuit voltage has no role to play in current carrying capability rating of a conductor. 14 is rated to to carry 15 amps in both 120, and 240 volt circuits.

If you go to Home Depot, Lowe's, etc., or Radio Shack, and ask for 12 AWG or "12 gauge" wire, they will know what to give you. AWG stands for "American Wire Gauge" and is a standard unit of measure for the diameter of the wire.

from wikipedia: By definition, No. 36 AWG is 0.0050 inches in diameter, and No. 0000 is 0.4600 inches in diameter. The ratio of these diameters is 92, and there are 40 gauge sizes from No. 36 to No. 0000, or 39 steps. Using this common ratio, wire gauge sizes vary geometrically according to the following formula: The diameter of a No. n AWG wire is...

active| newest | oldestfrom wikipedia:

By definition, No. 36 AWG is 0.0050 inches in diameter, and No. 0000 is 0.4600 inches in diameter. The ratio of these diameters is 92, and there are 40 gauge sizes from No. 36 to No. 0000, or 39 steps. Using this common ratio, wire gauge sizes vary geometrically according to the following formula: The diameter of a No. n AWG wire is...

http://en.wikipedia.org/wiki/American_wire_gauge