Ohmic Audio

Ohm's Law and Power

The foundation of all electrical work in car audio.

Ohm's Law:

V = I × R
I = V / R
R = V / I

Power:

P = V × I
P = I² × R
P = V² / R
Ohm's law reference diagram showing voltage at the top of a triangle, current and resistance at the base, plus matching power formulas for quick calculations
The triangle is a memory shortcut: cover the value you want to solve, then use the remaining positions to remember whether to multiply or divide voltage, current, and resistance.

Worked example — amplifier current draw:

A 500W RMS Class D amplifier (85% efficient) running from a 12V system:

P_input = P_output / η = 500 / 0.85 = 588W
I = P / V = 588 / 12 = 49A continuous

Add 25% safety margin for fuse and wire sizing:

I_design = 49 × 1.25 = 61A

Minimum wire gauge: 6 AWG (101A rated). Minimum fuse: 80A ANL.