"I run (x) amount of games without problems" is kinda vague when it comes to fire and safety. Different machines and devices, different loads. Finding how many machines a line can handle before an overload condition exists and trips a breaker isn't really a valid test either.

Get a Killawat meter as vic1900 said and plug a machine into it. Play a few games and record its watt usage. Divide by 120 (or 240 in those areas) for amperage. Repeat for each machine. Add the amperage for each machine and any other device together (lights, beer fridge, popcorn maker etc) for total line load.