Ohm's Law Power Conversion Voltage Root Solver
Watts to Volts Calculator — Voltage from Power & Resistance
Calculate required AC or DC driving voltage from power in Watts and load resistance in Ohms across any audio or electrical load.
Ohm's Law Voltage Sizing
Watts to Volts RMS Calculator
Calculate required AC RMS voltage, peak voltage, and current from known wattage and load resistance.
V_RMS = √(P · R) • V_Peak = V_RMS · √2 • V_p-p = 2 · V_Peak
100 W
8.0 Ω
Required True-RMS Voltage
28.28 V RMS
Instantaneous Peak Voltage: 40.00 V Peak
Peak-to-Peak Voltage (V_p-p): 80.00 V p-p
Continuous Current Draw (I_RMS): 3.535 Amperes
Multimeter Test Tone Setting:
VRMS = √(100 W × 8.0 Ω) = √800 = 28.28 V RMS
*Use this voltage target when setting amplifier gain with a True-RMS digital multimeter and a 0 dB sine wave test tone.
Interactive Engineering Reference
Ohm's Law & Electrical Power Formula Wheel
Click any quadrant of the formula wheel to solve for Power (P), Voltage (V), Current (I), or Resistance (R) with step-by-step mathematical substitutions.
Interactive Engineering Reference
P = (VRMS)² / R
Click any quadrant of the formula wheel to solve for Power (P), Voltage (V), Current (I), or Resistance (R) with step-by-step mathematical substitutions.
Result: 99.97 W P = (28.28 V)² / 8 Ω = 99.97 W
Ohm's Law Voltage Formulas (from Power & Impedance)
To determine the voltage required to push a specific wattage through an electrical load, use the square-root power formula derived from Ohm's Law:
Voltage Derivation Formulas
RMS Voltage: V_RMS = √(Power_Watts · Load_Resistance_Ohms)
From Current: V_RMS = Power_Watts / (I_RMS · Power_Factor)
Peak Voltage: V_Peak = V_RMS · √2 ≈ 1.4142 · V_RMS
Watts to Volts Reference Matrix Across Common Loads
| Target Power (Watts) | Voltage @ 1 Ω (Sub) | Voltage @ 2 Ω (Sub) | Voltage @ 4 Ω (Car/PA) | Voltage @ 8 Ω (Hi-Fi) | Voltage @ 16 Ω (Pro) |
|---|---|---|---|---|---|
| 10 Watts | 3.16 V RMS | 4.47 V RMS | 6.32 V RMS | 8.94 V RMS | 12.65 V RMS |
| 25 Watts | 5.00 V RMS | 7.07 V RMS | 10.00 V RMS | 14.14 V RMS | 20.00 V RMS |
| 50 Watts | 7.07 V RMS | 10.00 V RMS | 14.14 V RMS | 20.00 V RMS | 28.28 V RMS |
| 100 Watts | 10.00 V RMS | 14.14 V RMS | 20.00 V RMS | 28.28 V RMS | 40.00 V RMS |
| 250 Watts | 15.81 V RMS | 22.36 V RMS | 31.62 V RMS | 44.72 V RMS | 63.25 V RMS |
| 500 Watts | 22.36 V RMS | 31.62 V RMS | 44.72 V RMS | 63.25 V RMS | 89.44 V RMS |
| 1,000 Watts | 31.62 V RMS | 44.72 V RMS | 63.25 V RMS | 89.44 V RMS | 126.49 V RMS |
| 2,500 Watts | 50.00 V RMS | 70.71 V RMS | 100.00 V RMS | 141.42 V RMS | 200.00 V RMS |
Frequently Asked Questions
The formula is Voltage = √(Power × Resistance). For example, to deliver 100 Watts into an 8-Ohm speaker: V = √(100 × 8) = √800 = 28.28 Volts RMS.
When current is known: Voltage = Power (Watts) / Current (Amps). For example, 1,200 Watts drawing 10 Amps requires 1,200 / 10 = 120 Volts.
For 100W RMS into 8 Ohms (28.28 V RMS), the peak voltage is 28.28 × √2 = 40.00 Volts Peak (80.00 V peak-to-peak).
Because power equals V² / R, delivering the same 100 Watts into a lower impedance (like 4 Ohms) requires less voltage (20.0V RMS) but higher current (5.0A), whereas an 8-Ohm load requires 28.28V RMS and 3.54A.
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