Automotive Wiring Calculator
Pick the right wire gauge for automotive accessories based on current and run length.
How to Use
- Enter current (A), one-way run length (ft), and max allowable voltage drop (%).
- Recommended AWG is shown.
Inputs
Recommendation
Formulas
V-drop target
V_drop = V_system × drop%
Resistance
R = V_drop / I — total loop
Ω / 1000 ft
Copper: 10 AWG ~ 1 Ω · 14 AWG ~ 2.5 Ω
Fuse size
~125% of working current, but below wire ampacity
Frequently Asked Questions
Why one-way length?
Formula doubles it for the return path. Just enter how far the positive wire has to go to reach the load.
Voltage drop tolerance?
Most 12 V circuits: 3% = 0.36 V loss. Lighting, radio: 2%. Winch, starter: 5% acceptable.
Common Use Cases
Light bar
Sizing the feed wire from battery to switch to lights.
Amp install
Correct gauge for subwoofer amp power wire.
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