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Voltage Drop Calculator & Payback Planner

Estimate voltage drop, percent drop, line losses (kWh), and annual cost for single‑phase or three‑phase circuits. Then compare against an upsized conductor and see simple payback.

All math runs locally in your browser. No uploads. No tracking.

System

Duty & energy

Conductor & length

Size by AWG or mm² (no dataset; physics-based)

or
Advanced: reactance & direct resistance override

If you have a datasheet value (Ω per 1000 ft or per km), paste it here and enable the override. Otherwise the tool computes resistance from conductor area, material resistivity, and temperature.

Enter your details and select Calculate.

Method & assumptions
  • AWG formula (no lookup table): area in mm² = 0.012668 × 92^((36 − n)/19.5). We convert to m² for resistance.
  • Resistivity @ 20°C: Copper 1.724e−8 Ω·m, Aluminum 2.826e−8 Ω·m. Temperature coefficient: Cu 0.00393/°C, Al 0.00403/°C.
  • Voltage drop (resistive only): 1‑phase uses 2×I×Rcond, 3‑phase uses √3×I×Rphase. If reactance X is provided, uses I×(R cosφ + X sinφ) with the same geometric factor.
  • Losses: Resistive line loss P = I²×Rloop. Loop R is round-trip for 1-phase; for 3-phase, total copper loss is 3×I²×Rphase.
  • Payback uses your extra material/labor cost to upsize and compares annual energy savings.

About this free voltage drop calculator

This online voltage drop calculator estimates single‑phase and three‑phase voltage drop with power factor, optional reactance, AWG or mm² sizing, and copper or aluminum conductors. It also computes line losses in watts, converts them to kWh and annual cost, and shows the payback if you upsize wire. Everything runs locally in your browser.

Why voltage drop matters

Excessive drop wastes energy, overheats conductors, and can cause equipment issues. Many design guides target limits like 3 percent on branch circuits and 5 percent overall, but you must verify your local requirements and manufacturer recommendations.

Voltage drop & payback FAQ

Do I enter one-way or round-trip length?

Enter the one-way run. The tool handles round-trip internally for single-phase and total per-phase handling for three-phase.

Does power factor change the voltage drop?

Yes if you include reactance. With resistance only, PF does not change the magnitude of drop; including reactance uses R cosφ + X sinφ.

What if I only know resistance from a datasheet?

Use the override. Paste Ω per 1000 ft (or per km after converting) and set Use override = Yes.