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AWG Sizing Calculator

Find minimum wire gauge for current, length, and max voltage drop. Round-trip. SAE J1128.

Recommended gauge (AWG)

10

Voltage drop

0.328 V (2.73%)

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These calculators are engineering design aids intended for estimation and educational purposes. They do not replace professional engineering judgment or compliance with applicable standards (ABYC, NEC, IEC, SAE, or local regulations). Always verify final designs against relevant codes and manufacturer specifications.

What this tool does

This calculator helps determine the appropriate wire gauge (AWG) based on current (amps), length (meters), and maximum allowable voltage drop. It evaluates conductor size to meet a specified voltage drop target.

Voltage drop vs ampacity

Proper conductor selection must satisfy two constraints: (1) Voltage drop — conductor must be large enough to keep drop within acceptable percentage. (2) Ampacity — conductor must safely carry the intended current without overheating. This tool focuses on voltage drop sizing. Always verify conductor ampacity separately.

See fuse sizing to match protection to wire.

Marine & off-grid considerations

In marine environments: elevated ambient temperatures reduce ampacity; bundled conductors require derating; corrosion and vibration increase resistance at connections. Best practice: size for 3% drop on critical circuits, verify ampacity per applicable standard, consider future load expansion.

For house loads, use the battery runtime calculator.

Standards context

Common references include ABYC E-11 (marine), NEC ampacity tables, SAE automotive wiring standards. This tool provides a sizing estimate. Final design responsibility remains with the installer or engineer.

FAQ

What wire gauge do I need for 30 amps?
For 30A at 12V over 5m one-way with 3% max drop, you typically need AWG 10 or larger. Use the calculator with your exact current, length, and voltage to get the recommended gauge.
How does wire length affect gauge selection?
Longer runs increase resistance and voltage drop. For the same current and max drop percentage, longer runs require larger gauge. Double the length and you often need to go up 2–3 AWG sizes.
What is the 3% voltage drop rule?
ABYC E-11 recommends 3% max voltage drop for critical marine circuits (navigation, bilge, safety). At 12V that is 0.36V. Non-critical circuits may allow up to 10%.
Can I use mm² instead of AWG?
Yes. AWG and mm² are different sizing systems. This calculator uses AWG. For mm², convert using standard tables (e.g. AWG 12 ≈ 3.3 mm²).
Does temperature affect wire sizing?
Yes. Copper resistance increases with temperature. Engine rooms and underhood environments run hotter; derating may be required. This calculator assumes 20°C.

Related tools

Voltage Drop CalculatorFuse Sizing CalculatorBattery Runtime CalculatorMarine electrical guideMotorsport electrical guideTechnical whitepapersHome

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