RMS voltage is the effective value of an AC signal — the DC voltage that would deliver the same power to a resistive load. For a sinusoid: Vrms = Vpeak / √2.

How do I convert RMS to watts?

P = Vrms² / R, where R is the load resistance in ohms. You must know the impedance to calculate power.

What is the difference between RMS and peak voltage?

Vpeak is the maximum instantaneous voltage. Vrms = Vpeak / √2 ≈ Vpeak × 0.707. RMS is used for power calculations; peak is used for insulation and component ratings.

How many watts is 120V RMS into 8 ohms?

P = 120² / 8 = 1,800 watts. This assumes a purely resistive 8-ohm load and ideal operating conditions.

What impedance should I use for speakers?

Use the nominal impedance: typically 4Ω, 8Ω, or 16Ω. Actual impedance varies with frequency, but nominal is used for power ratings.

Vpp is the peak-to-peak voltage: the difference between the highest and lowest voltage in one cycle. Vpp = 2 × Vpeak.

RMS to Watts Converter

Convert RMS voltage to watts for any impedance. Bidirectional: Vrms→W, W→Vrms, Vpeak→Vrms. Shows Vpeak, Vpp, Irms, dBm, and dBW.

Mode

Vrms

Resistance (Ω)

Decimals

Power (Watts)

1,800.0000

Vrms² ÷ 8.0 Ω

Vrms

120.0000

RMS voltage

Vpeak

169.7056

Vrms × √2

Vpp

339.4113

Peak-to-peak

Irms (A)

15.0000

Vrms ÷ 8.0 Ω

dBm

62.55

10 × log₁₀(mW)

dBW

32.55

10 × log₁₀(W)

Vrms to Watts Table at 8.0 Ω

Vrms	Watts	Vpeak	Irms (A)	dBm
0.1	0.00	0.14	0.013	1.0
0.5	0.03	0.71	0.063	14.9
1	0.13	1.41	0.125	21.0
2	0.50	2.83	0.250	27.0
5	3.13	7.07	0.625	34.9
10	12.50	14.14	1.250	41.0
20	50.00	28.28	2.500	47.0
50	312.50	70.71	6.250	54.9
100	1,250.00	141.42	12.500	61.0
120	1,800.00	169.71	15.000	62.6
230	6,612.50	325.27	28.750	68.2
240	7,200.00	339.41	30.000	68.6
480	28,800.00	678.82	60.000	74.6

Common Load Impedances

Application	Impedance
Speaker (nominal)	4 Ω, 8 Ω, 16 Ω
RF systems	50 Ω
TV / Cable	75 Ω
Earphone	16–600 Ω
US mains	~14 Ω (15 A @ 120 V)

Planning notes, formulas, and examples

About the RMS to Watts Converter

The RMS to watts converter calculates electrical power from RMS voltage and impedance using the formula P = V²/R. It supports three modes: Vrms to watts, watts to Vrms, and Vpeak to Vrms to watts — covering every common voltage-to-power conversion scenario.

RMS (Root Mean Square) voltage is the effective voltage of an AC signal that delivers the same power as a DC voltage of the same value. This is the voltage reported by multimeters and used in power calculations for AC circuits.

Results include peak voltage, peak-to-peak voltage, RMS current, dBm, and dBW — essential for audio engineering, RF design, and electrical power analysis. A reference table at the selected impedance shows power for standard voltage levels from 0.1V to 480V. This makes the tool practical for bench testing, system sizing, and troubleshooting overloaded equipment. It is also useful when validating amplifier headroom, selecting safe speaker loads, and comparing datasheet ratings across manufacturers.

When This Page Helps

Audio engineers, RF technicians, and electricians need to convert between RMS voltage and power for speaker matching, amplifier design, and load calculations. This converter handles all the math for any impedance and helps prevent setup mistakes during equipment matching, commissioning, maintenance checks, and acceptance testing in the field. It keeps calculations repeatable and easier to review.

How to Use the Inputs

Select mode: Vrms→Watts, Watts→Vrms, or Vpeak→Vrms.
Enter the voltage or power value.
Enter the load impedance in ohms.
Read watts and all voltage equivalents.
Use presets for common scenarios (120V/8Ω, 1000W/4Ω).
Check the table for standard voltage-power pairs.

Formula used

P = Vrms² ÷ R. Vrms = √(P × R). Vpeak = Vrms × √2. Vpp = 2 × Vpeak. Irms = Vrms ÷ R.

Example Calculation

Result: 120 Vrms into 8 Ω = 1,800 W. Vpeak = 169.7 V. Irms = 15 A

P = 120² / 8 = 14,400 / 8 = 1,800 watts. Vpeak = 120 × 1.414 = 169.7 V. Irms = 120 / 8 = 15 A.

Tips & Best Practices

RMS voltage is what your multimeter reads for AC.
Vpeak = Vrms × √2 ≈ Vrms × 1.414.
Speaker power: P = Vrms² / impedance. An 8Ω speaker at 28.3V draws 100W.
US mains: 120 Vrms = 170 Vpeak = 340 Vpp.
EU mains: 230 Vrms = 325 Vpeak = 650 Vpp.
For RF: 50Ω is the standard impedance. 1 Vrms into 50Ω = 20 mW = 13 dBm.

RMS in Audio Engineering

Amplifier power ratings should specify RMS watts (continuous power into a specified impedance). "Peak watts" or "PMPO" ratings are marketing inflations. A 100W RMS amplifier into 8Ω delivers 28.3 Vrms. The same 100W into 4Ω needs only 20 Vrms — lower impedance means more current for the same power.

Why √2?

For a pure sine wave, the RMS value is the peak value divided by √2 ≈ 1.414. This factor arises from integrating the square of a sinusoid over one cycle. For non-sinusoidal waveforms (square, triangle, audio music), the relationship between peak and RMS differs.

AC Mains Worldwide

US: 120 Vrms / 60 Hz. Europe: 230 Vrms / 50 Hz. Japan: 100 Vrms / 50-60 Hz. The peak voltages are much higher: US peak = 170V, EU peak = 325V. Power electronics must handle these peak voltages even though RMS is quoted.

Sources & Methodology

Last updated: March 8, 2026

Frequently Asked Questions

RMS voltage is the effective value of an AC signal — the DC voltage that would deliver the same power to a resistive load. For a sinusoid: Vrms = Vpeak / √2.