Even an RMS reading meter will not give you a power factor corrected "real power" reading. You need to use either a power factor meter or the "three voltmeter" test as shown in
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A wattmeter will give you the actual wattage as well - unlike using a voltmeter and ammeter which only gives you volt-amps.
A simple Kill-A-Watt or Watts Up AC powermeter is very accurate.