Ohm's law states that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance: V = I × R. Combined with the power equation (P = V × I), you can calculate any two unknowns from any two knowns.

How does Ohm's law apply to speakers?

A speaker's nominal impedance (e.g. 8 ohms) determines how much current it draws from an amplifier at a given voltage. A 100W amplifier into 8 ohms produces 28.28V RMS and draws 3.54A. The same amplifier into 4 ohms would attempt to deliver 200W.

What is the difference between impedance and resistance?

Resistance is opposition to DC current (measured in ohms). Impedance includes resistance plus reactance from capacitors and inductors, and varies with frequency. A speaker's nominal impedance is its average impedance across the audio range.

Why is power proportional to voltage squared?

P = V²/R means that doubling the voltage quadruples the power. This is why a 6 dB increase in signal level (doubling voltage) results in 4× the power. In decibels, that's +6 dB voltage but only +6 dB power when the impedance stays the same.

AudioCalcs

Ohm's Law Calculator — Voltage, Current, Resistance & Power

Calculate voltage, current, resistance and power using Ohm's law for audio circuits.

Known Values

Voltage

Resistance

How We Calculate This

Ohm's Law

V = I × R

Power Equations

P = V × I = V² / R = I² × R

Given any two of V, I, R, P, the other two can be calculated.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard formulas. Always verify results for critical applications.