How many amps can a 18guage wire carry for 120VAC decorative lighting use Chrsistmas lights plugged end to end?

usually the box the lights come in tell you how many strands you can put together for 1 plug. the common number is 3 strings of lights per plug so if you get a power strip you can put 3 strings of lights in each plug and if it is a 4 plug power strip you can put 12 strings of light into the power strip