Amps to watts

Watts equal amps times volts, times the power factor on AC. Eight amps at 230 V with a power factor of 1 is 1,840 W. At a 0.8 power factor the same current is only 1,472 W of real power but still 1,840 VA of apparent power.

A clamp meter tells you current, not power, and the leap between them is where the power factor lives. For a kettle or heater the two are the same and the multiplication is exact. For a motor, a fluorescent ballast or an old switch-mode supply, current lags or distorts and real power can be well below the apparent figure. If you are estimating running cost from a clamp reading, an assumed power factor of 1 will overstate the bill for motor loads — a plug-in energy meter measures true power directly and settles the question.