How many 4 inch can lights can I run off 1 light switch? I have 12 lights to put in a kitchen and I wanted to know if I was going to need them on 2 light switches. Thanks Mark

There is more to it than how many you can put on a switch.

It's more like how many do you want on a switch. I would not want 12 lights on one switch. I'd rather see them broken up into sections.

If they are 4" cans, then they can likely take 75 watt lamps. 75x12 = 900
900 watts is fine on a 15A circuit, but it is too much for a standard 600 watts dimmer. It is even too much for a 1000 watt dimmer if it is in a box with other dimmers.

The direct answer to your question is up to 1800 watts of "fixture capacity" can be switched on a 15A circuit.