Voltage Drop Calculator

Compute voltage drop, percent drop, delivered voltage, and power loss for wire runs. Enter your system voltage, load current, distance, and wire size.

How to Use

  1. Enter your supply voltage and load current.
  2. Set the one-way distance and choose the distance unit.
  3. Select wire material and size (AWG/kcmil).
  4. Pick DC or AC mode (AC is an approximation; see Show Work).
Run Summary
Drop, delivered voltage, and loss update as you type.
Drop
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Drop %
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V at Load
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Loss
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Guidance: —
Inputs & Settings
Works fully in-browser. Share links are explicit (no URL changes while typing).
Common: 12V, 24V, 48V, 120V, 230V
Automotive often 5–60A; branch circuits typically 5–20A
This is one-way. Calculator uses round-trip length.
Use Auto if you already know total conductor resistance per 1000ft/m.
If Wire Size is not Auto, JS will populate a typical value you can override.
Used only in AC mode (approx.). Typical: 1.0 resistive, 0.8 motors.
Show Work (step-by-step)
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Work is shown in base units: volts (V), amps (A), ohms (Ω), watts (W), meters/feet for length.

Reference

Voltage drop is caused by wire resistance. For DC, a common approximation is: Vdrop = I × R_total. With round-trip wiring, R_total includes the outgoing and return conductors.

  • DC: Vdrop = I × R_total
  • Percent: %drop = (Vdrop / Vsupply) × 100
  • Delivered voltage: Vload = Vsupply − Vdrop
  • Power loss: Ploss = I² × R_total
  • AC (single-phase, approx.): uses PF to estimate effective current contribution (shown in work).
Tip: For critical loads, many workflows target ~3% drop. Higher drop can cause dim lights, slow motors, and heat.

FAQ

Why does the calculator use round-trip length?

In most DC circuits and single-phase AC circuits, current flows out and returns on another conductor, so total resistance is based on the full loop.

What if I only have one conductor length?

Uncheck “Use round-trip length” if your resistance input already accounts for the full loop or your scenario is different.

Is AC mode exact?

It’s an approximation meant for quick planning. Exact AC drop depends on reactance, conductor geometry, and load characteristics.

Tool Info

Last updated:

Updates may include additional wire tables, AC refinements, and edge-case handling.