Speaker RMS to Watts Calculator (Load Impedance to Power)
Determine actual continuous wattage and electrical current delivered into 2Ω, 4Ω, 8Ω, or 16Ω loudspeaker voice coils from measured RMS voltage.
Mode 1: RMS Voltage + Impedance
P = V² / RCalculate continuous electrical or speaker wattage using known RMS Voltage and load resistance/impedance.
Voltage × Load Impedance Power Matrix
Click standard test voltages and speaker impedances (2Ω, 4Ω, 8Ω, 16Ω) to immediately retrieve real continuous wattage.
Speaker Impedance & Power Delivery Physics
According to Ohm's Law and Joule's heating law, loudspeaker power dissipation is fundamentally governed by the relationship between alternating current voltage and voice coil load impedance:
Where V_RMS is the amplifier output voltage in Volts RMS, and R is the nominal voice coil impedance in Ohms (Ω).
Voltage, Impedance & Power Reference Matrix
| Output Voltage (V_RMS) | 2 Ω Load (Subwoofer) | 4 Ω Load (Car / PA) | 8 Ω Load (Home Hi-Fi) | 16 Ω Load (Horn / Pro) |
|---|---|---|---|---|
| 10.0 V RMS | 50.0 Watts (5.00 A) | 25.0 Watts (2.50 A) | 12.5 Watts (1.25 A) | 6.25 Watts (0.63 A) |
| 14.14 V RMS | 100.0 Watts (7.07 A) | 50.0 Watts (3.54 A) | 25.0 Watts (1.77 A) | 12.5 Watts (0.88 A) |
| 20.0 V RMS | 200.0 Watts (10.0 A) | 100.0 Watts (5.00 A) | 50.0 Watts (2.50 A) | 25.0 Watts (1.25 A) |
| 28.28 V RMS | 400.0 Watts (14.1 A) | 200.0 Watts (7.07 A) | 100.0 Watts (3.54 A) | 50.0 Watts (1.77 A) |
| 40.0 V RMS | 800.0 Watts (20.0 A) | 400.0 Watts (10.0 A) | 200.0 Watts (5.00 A) | 100.0 Watts (2.50 A) |
| 63.25 V RMS | 2,000.0 Watts (31.6 A) | 1,000.0 Watts (15.8 A) | 500.0 Watts (7.91 A) | 250.0 Watts (3.95 A) |
Understanding Power Compression in Loudspeakers
When an amplifier sends high continuous wattage to a speaker, the copper wire in the voice coil converts approximately 98% of that electrical energy into heat (since typical loudspeaker acoustic efficiency is only 1% to 2%).
Because copper has a positive temperature coefficient of resistance (+0.393% per °C), heating a voice coil from 20°C to 150°C increases its resistance from 8.0 Ω to approximately 12.1 Ω. This phenomenon—known as power compression—causes the speaker to draw less current, reducing acoustic output by 1.5 dB to 3.0 dB under heavy sustained loads.