Voltage Drop Calculator

Our voltage drop calculator helps electricians and engineers ensure proper wire sizing. Calculate voltage loss over distance, verify NEC compliance, and optimize wire gauge selection for residential and commercial installations.

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New
⚡
240V
WIRE
100 ft
💡
232V
V
A
ft

Results

7.74
Volts dropped
⚠️ Exceeds 3% NEC recommendation
Drop %
3.23%
At Load
232.26V
Recommended Wire
8 AWG

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straighten NEC Recommendations

Branch Circuit ≤ 3%
Feeder + Branch ≤ 5%
Sensitive Equipment ≤ 2%

science K Factor (Resistivity)

Copper 12.9
Aluminum 21.2

The Formula

Voltage drop increases with current, length, and wire resistance. NEC recommends max 3% drop for branch circuits and 5% total for feeder + branch.

VD = (2 × K × I × L) / CM (single-phase)

lightbulb Variables Explained

  • VD Voltage drop (V)
  • K Resistivity constant (12.9 for copper, 21.2 for aluminum)
  • I Current (A)
  • L One-way length (ft)
  • CM Circular mils of conductor

tips_and_updates Pro Tips

1

NEC recommends max 3% voltage drop for branch circuits

2

Total voltage drop (feeder + branch) should not exceed 5%

3

Copper has lower resistance than aluminum

4

Larger wire gauge = lower voltage drop

5

Three-phase has lower drop than single-phase for same power

6

Temperature affects conductor resistance

Frequently Asked Questions

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voltage drop calculator wire voltage loss electrical calculator nec voltage drop wire gauge calculator cable sizing electrical wiring nec 3% voltage drop
verified

Data sourced from trusted institutions

All formulas verified against official standards.

NEC (National Electrical Code) open_in_new