Enter your current, one-way distance, and system voltage — we'll recommend the smallest safe wire gauge that also keeps voltage drop under 3%.
This picks the smallest gauge satisfying both a 3% voltage-drop target and standard NEC ampacity — always confirm against your local code and insulation rating.
Two different limits govern wire sizing: the wire has to carry the current without overheating (ampacity), and it has to deliver the current without wasting too much voltage over distance. On short, high-current runs ampacity usually wins; on long, low-current runs voltage drop usually wins. This tool checks both and recommends whichever is stricter — use the voltage drop calculator to see the exact numbers for a specific gauge.
For short runs under about 15 feet, ampacity is usually the limiting factor. Past that, voltage drop typically takes over, especially on 12V systems where 3% is a small margin.
Going one size larger than the minimum is common practice and cheap insurance against future load increases or slightly longer runs than measured.