# AC Voltmeter

I took some measurements for a Physics lab and don't recall whether the Voltmeter I used reports the peak voltage or rms voltage. I need rms voltage to calculate the rms current. Can anyone tell me what the norm is for voltmeters: peak or rms?

To divide by the [squ]2 or not to divide by the [squ]2, that is the question.

Thanks.

## Answers and Replies

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jamesrc
Gold Member
My guess, RMS.

Hey, that rhymed.

If it was giving you a steady reading for AC voltage, it was probably RMS.

chroot
Staff Emeritus
Gold Member
Actually, the vasssssst majority of AC voltmeters are peak-to-peak. Some of them which say "RMS" actually only give the correct RMS voltage at one frequency, usually 60 Hz. Only a meter which says "true RMS" will actually give you the RMS amplitude at all frequencies.

Just because the meter is not true RMS does not mean it will not give a steady reading -- it will. It'll just be an incorrect steady reading.

- Warren

jamesrc