RMS to Watts Converter

Convert RMS voltage or current into watts for a given load, with peak and peak-to-peak values.

Power9.99 W8.94 V RMS into 8 ohm

RMS voltage8.94 V

RMS current1.1175 A

Peak voltage12.6431 Vsine wave — RMS x 1.414

Peak-to-peak25.2861 V

Peak power19.981 Winstantaneous, not continuous

8.94 V RMS into different loads

Impedance	Power	Current
2 ohm	39.96 W	4.47 A
4 ohm	19.98 W	2.235 A
6 ohm	13.32 W	1.49 A
8 ohm	9.99 W	1.118 A
16 ohm	5 W	0.559 A

Why RMS is the value that matters

An alternating voltage spends most of its cycle below its peak, so the peak figure overstates how much work it does. The RMS (root mean square) value is the equivalent steady DC voltage that would deliver the same power — which is exactly why power calculations use it:

P = V_RMS × I_RMS = V_RMS² ÷ R = I_RMS² × R

8.94 V RMS into 8 ohms is 8.94² ÷ 8 = 10 W.

Peak, RMS and the factor 1.414

For a sine wave specifically:

V_peak = V_RMS × √2 ≈ 1.414 × V_RMS
V_RMS = V_peak ÷ √2 ≈ 0.707 × V_peak
Peak-to-peak is twice the peak.

That √2 is the crest factor of a sine wave and nothing else. Square waves have a crest factor of 1, triangle waves √3, and music is far higher and constantly changing — so applying 1.414 to an audio signal is wrong.

Impedance is not resistance

A speaker's rated impedance is a nominal figure; the real value swings widely with frequency, often dipping well below the number on the label. Amplifier power ratings assume the nominal value, which is why the same amp delivers different real-world power at different frequencies.

Beware “peak music power” or “PMPO” on consumer equipment. Only continuous RMS power into a stated impedance is comparable between products.