How it’s calculated
- VD = 2 × 12.9 × amps × length ÷ cmil (copper)
Worked example
16 AWG cord, 50 ft, 12 A tool at 120 V.
Inputs
- Cord gauge
- 16 AWG
- Cord length
- 50 ft
- Tool or appliance current
- 12 A
- Outlet voltage
- 120 V
Results
- Voltage drop
- 5%
- Voltage at the tool
- 114 V
- Voltage drop
- 5.99 V
Assumptions and limits
- Stranded copper cord; outlet voltage is steady under load.
Verify the result against the applicable local code, adopted code edition, manufacturer instructions and project requirements. See our methodology.
Questions
What gauge extension cord for 100 feet?
For a 12–15 A tool at 100 ft, 12 AWG keeps drop near 5%; 10 AWG keeps it lower.
Is a lower gauge number thicker?
Yes. 12 AWG is thicker than 16 AWG and carries current with less drop.