ToolsElectronics, cables & data
Ohm's law & power
Voltage, current, resistance and power from any two of them, e.g. amplifier watts into a speaker load.
Ω
W
Voltage (RMS)
28.28 V
Current (RMS)
3.536 A
Resistance / impedance
8 Ω
Power
100 W
Voltage as level
31.25dBu
Peak voltage (sine)
40 V
For amplifiers and loudspeakers, use RMS voltage and the nominal impedance: 100 W into 8 Ω needs 28.3 V RMS (40 V peak). Real speaker impedance varies with frequency.
How it works
Two of the four quantities determine the other two. For audio, use RMS voltages and the nominal impedance of the load to estimate amplifier power and the voltage it must swing.
Formulas
- V = I · R
- P = V · I = V² / R = I² · R
Found a mistake or have an idea for this tool?
Suggest a change