calctric.

USE ONLINE · FREE · NO SIGNUP

Voltage-drop estimate

A quick look at the effect of wire size and run length. This free tool uses the app’s basic K-factor method.

CALCTRIC / VOLTAGE

One set of conductors. Enter the one-way route; the circuit factor accounts for the return path. Three-phase inputs are line voltage and line current.

K-factor estimate · no code tables

YOUR RESULT

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Estimate only. This result does not check ampacity or establish code compliance.

Calculation details

Private by design. Calculations run on this device. No account or saved web history.

Need regional tables and more solve modes? Explore Voltage Drop in the app ↗

HOW TO USE IT

From inputs to insight.

  1. Select AC two-wire, balanced three-phase or DC two-wire, then conductor material and size.
  2. Enter the supply voltage, actual load current and one-way route length. Switching feet/metres preserves the length.
  3. Read estimated drop in volts and percent, plus estimated load voltage. Change a value to compare another scenario.
  4. Use the app’s full regional methods when you need CEC or NEC data and supported sizing workflows. Independently check the installation.

WORKED EXAMPLE

20 A over 100 feet.

Use AC · 2-wire, 120 V, 20 A, 100 ft and 12 AWG copper. With K = 12.9 and 6,530 circular mils, drop = 2 × 12.9 × 20 × 100 ÷ 6,530.

The estimate is 7.90 V (6.58%), leaving about 112.10 V at the load. This is an illustration, not a conductor-sizing recommendation.

Know what the answer means.

Uses K = 12.9 for copper or 21.2 for aluminum and the same circular-mil sizes as the app’s K-factor estimate. Drop = circuit factor × K × current × one-way feet ÷ circular mils. Circuit factor is 2 for two-wire AC/DC or √3 for balanced three-phase.

This is a resistance-only approximation. It does not model actual conductor temperature, AC reactance, power factor, raceway effects, connections, parallel sets or upstream drop. It is not a CEC 2024 table calculation or an NEC table calculation. There is no automatic pass/fail or wire-size recommendation.

Verify actual conductor data, equipment voltage requirements, ampacity, protection and locally adopted codes. The full app’s Voltage Drop tool is Premium; this basic web estimate is free.

Calculation aids can contain errors. Verify inputs and real conditions independently. Read our terms and safety disclaimer.

COMMON QUESTIONS

Make sense of the result.

Do I enter one-way length or the total wire length?

Enter the one-way route from the supply to the load. Do not double it for the return conductor: the factor of 2 handles the two-wire AC/DC circuit. Balanced three-phase uses a factor of √3 with line-to-line voltage and line current.

Is this a CEC or NEC voltage-drop calculation?

This browser tool uses the basic K-factor estimate available in the app. It does not use CEC or NEC table data and does not certify code compliance. The Premium app tool offers the supported regional methods and additional solve modes.

Why can the result differ from the full app calculator?

Use the same K-factor method, material, wire size, circuit, current and length for a like-for-like comparison. Regional table methods and published impedance can reflect conditions that this simple resistance-only estimate does not model.

Can this tell me which wire size is safe?

No. You can compare the estimated voltage drop of different sizes, but this tool does not check ampacity, protection, terminal ratings, installation conditions or local requirements. It does not recommend a compliant conductor size.

Why are voltage and percentage results rounded?

The displayed voltage drop, drop percentage and load voltage round to two decimal places for readability. Calculations retain full precision. A very small nonzero result can display as 0.00; display rounding does not mean a conductor has no resistance.