Free Wire Gauge & Voltage Drop Calculator
Determine circuit voltage loss, conductor heating, and the ideal AWG or mm² wire size for DC solar, automotive, and AC mains runs.
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📊 Voltage Drop Results
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Why Voltage Drop Matters in DC & AC Circuits
All physical wires possess electrical resistance. When electric current flows through a conductor, Ohm's law dictates that a portion of the source voltage is lost along the run: $V_{drop} = I imes R_{loop}$. In low-voltage systems (like 12V camper vans, solar arrays, or trolling motors), a small 1V drop represents a massive 8.3% loss, causing inverters to trip off and motors to overheat.
NEC 3% and 5% Code Rules
The National Electrical Code (NEC 210.19) recommends that maximum voltage drop should not exceed 3% on any branch circuit, and the combined feeder plus branch circuit should not exceed 5% for optimal efficiency.
Remember the Roundtrip Loop
Current must travel down the positive line AND return via the negative ground wire. A 25-foot distance to an appliance means the current must traverse 50 feet of physical conductor.
Frequently Asked Questions
Why is voltage drop so much worse on 12V than 120V?
To deliver 120 Watts of power on a 120V line requires only 1 Amp of current ($P = V \times I$). On a 12V system, that same 120W load demands 10 Amps (10x current). Because voltage drop and heat loss scale with current ($V = IR, P = I^2 R$), 12V systems suffer dramatically higher voltage loss over distance.
What is the resistance difference between copper and aluminum wire?
Copper has a resistivity of approximately 10.4 ohms per circular mil-foot, whereas aluminum is roughly 17.0 ohms (aluminum is ~61% as conductive as copper). You generally need to upsize aluminum wire by two AWG gauge sizes to match copper's ampacity and voltage drop performance.
What wire gauge do I need for a 12V 1000W inverter?
A 1000W inverter running near full load pulls approximately 85 to 100 Amps from a 12V battery. For a short 3-foot to 5-foot run, you need minimum 2 AWG or 1/0 AWG welding cable to keep voltage drop below 2% and prevent low-voltage inverter cutoffs.