GMK’s Power Wire Gauge & Voltage Drop Calculator

This calculator estimates voltage drop, heat loss, and conservative wire rating using common AWG resistance values. It also includes an amp draw estimator and fuse sizing helper for real-world car audio installations.

Wire Size Calculator

Estimated current (amps):

If you don’t know amps, use the Amp Draw Estimator.

One-way length (feet):

Measure like the wire would actually route (not “straight line”).

Use round-trip length (power + ground)

Chassis return (common installs)

System voltage (V):

14.4V typical, 15.2V LTO same-rail, 16V+ systems vary.

Wire size:

CCA wire (not OFC)

Parallel runs:

Multiple runs act like “bigger wire” (if grounds and terminations are solid).

Target max drop:

Lower % = less heat + less dimming. Power wire guys usually aim 3–5%.

Amp Draw Estimator

If you know RMS watts and voltage, this gives a ballpark average draw while playing.

Using system voltage from above: 14.4 V.

Total RMS watts (sub + mids/highs): Amp efficiency:

Music factor:

Real-world amps: clamp meter on the charge wire, or some vehicles show it in OBD apps. This estimator is for “close enough to not light money on fire.”

Fuse Size Estimator

Suggests fuse for power wire at battery, based on peak draw and wire capacity.

Peak current draw (A):

Use worst-case from Amp Draw Estimator above.

Wire size:

CCA wire (not OFC)

Parallel runs:

Fuse protects wire from shorts. Size to expected max + margin, but ≤ wire rating. Common ANL sizes: 50,80,100,150,200,250,300A+.

Reminder: voltage drop = heat + lost power. If a wire is getting hot, it’s not “normal” — it’s a problem.

“Should I use round-trip?” - If you’re guessing, use round-trip. It keeps the result conservative and prevents under sizing.

“What’s chassis return estimate?” - A conservative penalty for using the vehicle body as the ground path. Real results depend on how solid your grounds are.

“What fuse should I run?” - Pick the fuse based on the wire rating, not your wattage. Fuse goes right at the power source.

“Why does CCA show worse results?” - It’s aluminum with a copper jacket - higher resistance means more loss. That’s why CCA needs bigger gauge (or more runs) to match OFC.