Proper wire sizing ensures safety and efficiency. Undersized wires can overheat, while oversized wires waste money. Consider both ampacity and voltage drop.
Wire Size Calculator
Our wire size calculator helps electricians, engineers, and DIY enthusiasts select the appropriate wire gauge for any electrical project. Enter your circuit parameters to get recommended wire sizes that meet electrical code requirements while minimizing voltage drop and power loss.
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Updated: April 2025
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Recommended Wire Size
10
AWG
5.26 mm² cross-section
Wire Specifications
Voltage Drop
2.5%
Actual Drop
6.0 V
Wire Resistance
0.15 Ω
Ampacity
30 A
Power Loss
60 W
Common AWG Sizes
14
15A
12
20A
10
30A
8
40A
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Powered by ClaudeEnter your values and calculate to receive AI-powered insights about your results.
cable AWG Ampacity (Copper)
14 AWG
15A
12 AWG
20A
10 AWG
30A
8 AWG
40A
6 AWG
55A
warning NEC Voltage Drop
- 📏 Branch circuits: Max 3%
- 🔌 Feeder + Branch: Max 5%
- 🔧 Aluminum needs 1-2 sizes larger
How to Use This Calculator
1
Enter Current
Input the maximum current (amps) your circuit will carry
2
Select Voltage
Choose your system voltage (120V, 240V, etc.)
3
Enter Distance
Input one-way distance from panel to load
4
Choose Material
Select copper or aluminum conductor
5
Review Results
See recommended wire size and voltage drop analysis
The Formula
Wire size is determined by ampacity (current carrying capacity) and acceptable voltage drop. NEC recommends max 3% voltage drop for branch circuits and 5% total for feeder + branch combined.
Voltage Drop = (2 × L × I × R) / 1000
lightbulb Variables Explained
- L One-way wire length in meters
- I Current in amperes
- R Wire resistance in Ω/km
tips_and_updates Pro Tips
1
Always size wire for both ampacity AND voltage drop requirements
2
Use the larger wire size if ampacity and voltage drop calculations differ
3
Copper has better conductivity but aluminum is lighter and cheaper for large runs
4
Derate ampacity for bundled wires or high ambient temperatures
5
NEC allows max 3% voltage drop for branch circuits
6
For long distances, consider increasing wire size to reduce power loss
7
Always follow local electrical codes and permit requirements
Common sizes: 14 AWG (15A), 12 AWG (20A), 10 AWG (30A), 8 AWG (40A), 6 AWG (55A). Aluminum requires 1-2 sizes larger than copper for the same ampacity.
Frequently Asked Questions
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Data sourced from trusted institutions
All formulas verified against official standards.