Voltage Drop Calculator

Calculate voltage drop, wire size, maximum current, and wire length for DC, single-phase, and three-phase circuits.

Your Input

Select a calculation type, enter your circuit parameters, then click Calculate to see voltage drop, wire size, max current, or max length with step-by-step solution.

Complete User Guide

What is Voltage Drop?

Voltage drop is the reduction in voltage in an electrical circuit due to the resistance of the conductors. It's important to keep voltage drop within acceptable limits to ensure proper equipment operation. The NEC recommends no more than 3% for branch circuits and 5% for combined feeder and branch circuits.

Key Formulas

DC: VD = I × R × 2

Single-Phase AC: VD = I × R × 2 × PF

Three-Phase AC: VD = I × R × √3 × PF

Resistance: R = (ρ × L) / A

4 Calculation Types

Voltage Drop

Calculate voltage loss in a circuit from current, wire size, and length.

Wire Size

Find the minimum AWG wire size for a target maximum voltage drop.

Maximum Current

Calculate the maximum current you can draw within a voltage drop limit.

Maximum Length

Calculate the maximum wire run length within a voltage drop limit.

How to Use

  1. Select a calculation type (Voltage Drop, Wire Size, Max Current, or Max Length).
  2. Enter circuit parameters: voltage, current, wire length, wire size, and material.
  3. Choose the circuit type (DC, Single-Phase AC, or Three-Phase AC).
  4. Click Calculate to get results with step-by-step NEC-compliant solutions.

Wire Materials

Copper: Lower resistance (12.9 Ω-cmil/ft), higher cost — standard for residential wiring.

Aluminum: Higher resistance (21.2 Ω-cmil/ft), lower cost — common in large feeder runs.

Important Notes

  • NEC recommends ≤ 3% drop for branch circuits, ≤ 5% total.
  • Voltage drop increases with wire length and current.
  • Larger wire sizes (lower AWG number) reduce voltage drop.
  • Always follow local electrical codes and consider temperature derating.

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