Respected sir I amprakash ihave doubt regarding load calculation.

I have a 5 amp socket (ups power ) .can I connect 5 computors to that socket through extension box.please explain me any body knows

Need to know the load in amps or watts of each computer. If the total exceeds 5 amps, then, no.

If in the USA, and possibly elsewhere, the receptacle may need to be derated, here in the US we derate certain things by 80%.

Also need to know the wattage, amperage or volt-amps output capacity of the UPS , to be sure it is not exceeded.

As the reply before me states, this will depend a lot on the computers. However, unless you dumped a lot of cash on that UPS, 5 computers (unless they're laptops or other ultra low power systems) will probably kill it before you can snap your fingers. The battery just doesn't have that kind of capacity.