12 Volt Wire Size Calculator
Preset to 12 V. Adjust load current, run length, drop %, and material.
How to Use This Calculator
Tailored for 12 V systems (automotive/RV/solar). Enter load current, one-way length, allowable drop %, and material. Voltage is preset to 12 V but can be adjusted for 12.6–14.4 V charging systems.
- Low voltages are sensitive to drop—use conservative drop % (e.g., 3%).
- Enter one-way length; return path is included automatically.
Formula
Vdrop = I · R = I · (ρ · 2L / A)
A ≥ ρ · 2L · I / Vdrop,allow
For 12 V systems, small absolute drops can be a high percentage of supply voltage. Choose larger conductors for long runs or high currents.
Frequently Asked Questions
Is copper preferred for 12 V systems?
Copper offers lower resistance per cross-section and is commonly used in automotive and RV wiring for reduced voltage drop.
What drop percentage should I use?
3% is a common target for critical loads. For non-critical loads, up to 5% may be acceptable.