About

In circuit design and audio engineering, matching voltage to the power rating of a component is critical for safety and longevity. If you know the power rating (in Watts) of a resistor or a speaker, and its resistance (in Ohms), you need to know the maximum voltage it can handle before it sustains damage.

This tool calculates the voltage derived from the Power-Resistance relationship. It is particularly useful for verifying if a specific power supply rail will overheat a resistor, or for calculating the RMS voltage required to drive a speaker to its full potential without blowing the voice coil.

Formulas

The formula is derived by substituting Ohm's Law into the Power Law (P = V×I).

V = √P × R

Where:

P is Power (Watts).
R is Resistance (Ohms).

Reference Data

Component Type	Typical Power Rating (P)	Typical Resistance (R)	Max Safe Voltage (V)
Standard Resistor	0.25 W	1 kΩ	15.8 V
Power Resistor	5 W	10 Ω	7.07 V
Headphones	0.05 W (50mW)	32 Ω	1.26 V
Car Speaker	50 W	4 Ω	14.1 V
PA Subwoofer	1000 W	8 Ω	89.4 V
Heater Element	1500 W	10 Ω	122.5 V

Frequently Asked Questions

For DC circuits, it is the constant DC voltage. For AC (audio/mains), the result is the RMS (Root Mean Square) voltage. If you need the Peak voltage for an AC signal, multiply the result by approx 1.414.

Lower resistance draws more current. Since Power is Voltage times Current, if Current increases easily (due to low resistance), you need less Voltage to achieve the same Wattage.

The component will dissipate more power than it is rated for. This leads to rapid heating, physical damage (burning), and an open circuit failure.