If you are careful to avoid high power draining devices (heaters, motors, refrigerators, AC units, etc) and are sure that nothing else but your computers are on said 15 amp circuit (generally an entire room or sometimes even two rooms may be on the same circuit) then it is POSSIBLE to run 5 computers and 5 LCD monitors on a single circuit. But very little else. Figure each computer will be around 250 watts... that is 1250 - within the limits for continual use. This is assuming a "normal" computer setup and a low power LCD monitor. Use a CRT and also put a refrigerator or other high amp devices on the same circuit and you will most likely trip. Any lights, particularly high energy incandescents will use . 40 - 60 watts EACH. This can add up quickly and put you over the edge.

Add everything up that is plugged in. Every device will have its power consumption listed on it, either in Amps (multiply that by 120 to get watts) or in watts. It would be helpful to read the actual power use from the wall though and add all of those up.

Note that you can push this further as some of you are likely doing. You can run 2000 watts on a 15 amp breaker. You can also swim with sharks. It SHOULD eventually trip (to save your house/life). However, if this is very stupid to do. If the breaker fails to trip, you could start a fire. I DO NOT suggest that you push the envelope when it comes to electrical use. There are codes and limits for a reason. You can jury rig things with a PROPERLY RATED extension cord but if in doubt, consult a professional.