AWG Wire Gauge & Voltage Drop Calculator
Determine code-compliant AWG wire size and calculate voltage drop across wire runs.
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How to Use the Wire Gauge Calculator: AWG Sizing & Voltage Drop Limit
- 1Select your circuit voltage (e.g. 12V DC automotive/marine, 120V household AC, or 240V heavy appliance).
- 2Input the continuous circuit current load in Amperes (Amps).
- 3Enter the one-way distance from the breaker panel to the electrical load in feet.
- 4Review your recommended AWG wire gauge, actual voltage drop in volts and percentage, and NEC compliance.
Formula & How It Works
Circular Mils & Voltage Drop Formulas
Calculates conductor resistance and required circular mil area.
Worked Examples
120V Circuit at 20 Amps Running 60 Feet
Input: Voltage: 120V, Current: 20A, Distance: 60 ft, Copper, Max Drop: 3.0%
Explanation: While #12 AWG handles 20A thermally, upsizing to #10 AWG prevents the 60-foot run from exceeding the 3% voltage drop threshold.
Frequently Asked Questions
Why does the NEC recommend keeping voltage drop under 3%?▼
Keeping branch circuit voltage drop below 3% (and total feeder plus branch below 5%) ensures motors, computers, and appliances run efficiently without overheating or flickering.
How does wire gauge numbering work?▼
In American Wire Gauge (AWG), smaller numbers represent thicker wires with lower electrical resistance (e.g. #10 AWG is thicker and carries more current than #14 AWG).
Can I use aluminum wire instead of copper?▼
Yes, but because aluminum has higher electrical resistance, you must typically upsize by one to two AWG sizes compared to copper.
Why is voltage drop so much more severe in 12V DC systems?▼
In a 12V circuit, a 1-volt drop represents over 8% of total system voltage, causing lights to dim and electronics to shut down.
Quick Reference & Conversion Table
| Circuit Amperage | Standard Breaker Gauge | Max Run at 120V (<3% Drop) | Max Run at 240V (<3% Drop) |
|---|---|---|---|
| 15 Amps | #14 AWG Copper | 50 Feet | 100 Feet |
| 20 Amps | #12 AWG Copper | 60 Feet | 120 Feet |
| 30 Amps | #10 AWG Copper | 65 Feet | 130 Feet |
| 50 Amps | #6 AWG Copper | 85 Feet | 170 Feet |
⚠️ Common Pitfalls to Avoid
- •Failing to account for distance when sizing wire (a gauge that is safe for a 10-foot run may cause severe voltage drop over 100 feet).
- •Confusing two-wire distance with one-way distance in calculation formulas.
💡 Practical Real-World Uses
- •Sizing wire runs for detached garage subpanels, well pumps, and electric vehicle (EV) home chargers.
- •Wiring 12-volt solar panels, marine trolling motors, and camper van electrical systems.
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