RMS to Watts Converter
Convert RMS voltage to watts for speakers, amplifiers, and AC circuits. Three solvers: resistive (P = Vrms²/R), true AC power (P = Vrms × Irms × PF), and reverse solve (find R or Vrms from watts).
Worked examples
| Case | Math | Result |
|---|---|---|
| 120 Vrms into 8 Ω (amplifier / mains) | 120² / 8 = 14400 / 8 | 1800 W |
| 70.71 Vrms into 4 Ω (pro audio) | 70.71² / 4 = 4999.90 / 4 | 1249.98 W ≈ 1250 W |
| 230 V, 5 A, PF 0.85 (appliance) | 230 × 5 × 0.85 | 977.5 W |
| 1000 W amp into 8 Ω → Vrms needed | √(1000 × 8) = √8000 | 89.44 Vrms |
Formulas and when to use them
Resistive mode — P = Vrms² / R. Use when the load is a resistor or a loudspeaker driven by an amplifier (the standard audio "RMS watts" rating). Speaker impedance (4 Ω, 8 Ω) plays the role of R.
AC mode — P = Vrms × Irms × PF. Use for mains-powered equipment with reactive components (motors, transformers, SMPS). PF below 1 means part of the current does no useful work.
RMS (root mean square) is the DC-equivalent heating value of an AC waveform. Do not plug peak or peak-to-peak voltage into these formulas — convert to RMS first.
FAQ
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Free tool by NRTechStudio