Voltage Drop Calculator with Amps, Ohms & Percentage Output

Voltage Drop Calculator for Wire Size & Length Selection

A Voltage Drop Calculator for wire size and length selection estimates how much voltage is lost along a conductor so you can choose an appropriate wire gauge and avoid underperformance or safety issues.

What it does

• Inputs: supply voltage, load current (amps), conductor length (one-way or round-trip), conductor material (copper or aluminum), wire gauge or cross-sectional area, number of phases (single- or three-phase), and optionally acceptable voltage drop percentage or target voltage at load.
• Outputs: voltage drop (volts), voltage at load (volts), percent voltage drop, recommended wire gauge (or confirmation that a given gauge is acceptable), and power loss (watts).

Key formulas

• Single-phase voltage drop (approximate):
  Vdrop = I × R × L × 2
  where I = current (A), R = resistance per unit length (Ω/ft or Ω/m), L = one-way length.
• Three-phase line-to-line (approximate):
  Vdrop = √3 × I × R × L
• Percent voltage drop = (Vdrop / supply voltage) × 100%
• Power loss = I × Vdrop

(Resistance per unit length depends on conductor material and gauge; use standard tables or manufacturer data.)

Typical design limits

• Common target: keep voltage drop ≤ 3% for branch circuits and ≤ 5% for combined feeder + branch limits.
• For long runs or high-current loads, upsize conductor to reduce drop or use higher supply voltage.

Practical steps to use the calculator

1. Choose material: copper or aluminum.
2. Enter supply voltage and whether system is single- or three-phase.
3. Enter load current (amps) or load power (watts) — calculator can convert watts to amps.
4. Enter one-way conductor length (specify units).
5. Enter candidate wire gauge(s) or let the tool recommend a gauge for a target percent drop.
6. Review Vdrop, percent, and power loss; if percent > target, increase wire size or reduce length.

When to check other factors

• Temperature, conduit fill, and bundling affect ampacity (not directly voltage drop) but may require different gauge for safety.
• In motor or sensitive electronic loads, consider starting currents and voltage tolerance.
• For long DC runs (solar, battery systems), perform same calculation but use DC resistance values.

Quick recommendations

• For runs under ~50 ft at typical household currents, standard branch-circuit gauges (14–12 AWG) usually keep drop within limits; for longer runs upsize one or two gauges.
• For runs over 100 ft or heavy loads, calculate precisely and likely use larger conductors or higher supply voltage.

If you want, I can calculate voltage drop for a specific scenario (supply V, amps, length, material, and desired max % drop).