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Two-Conductor Voltage Drop Calculator

Estimate two-conductor voltage drop in volts and percent from current, one-way run length, system voltage, and known conductor resistance.

Content updated October 7, 2026 · Details

Published

Content updated

Recorded calculation check · Verification scope

Voltage drop

Inputs ↓
Voltage loss
3.09 V
Voltage drop percentage
2.57%

Arithmetic worksheet only. Enter resistance from the conductor manufacturer; this does not size conductors or determine ampacity or code compliance.

V
A
ft
Ω/1000 ft

Results update as you type.

Result links include your inputs in the URL. Anyone with the link can read them; avoid sharing sensitive values.

Compare scenarios

Save a result, change your inputs, then compare. Up to three saved scenarios for this visit.

Worked example

voltage: 120 · current: 16 · length: 50 · resistance: 1.93

Result: 3.09 V

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Estimate two-conductor voltage drop in volts and percent from current, one-way run length, system voltage, and known conductor resistance.

Inputs and method

Enter voltage, current, one-way run length, and candidate-conductor resistance in ohms per 1,000 feet. For a two-conductor path, voltage drop is 2 × current × resistance × one-way length ÷ 1,000; percentage drop divides that result by system voltage.

Voltage drop and percentage are calculated before rounding the displayed results to two decimals.

Worked example

For a 120 V system carrying 16 A over a 50 ft one-way run, with resistance of 1.93 ohms per 1,000 ft, voltage drop is 2 × 16 × 1.93 × 50 ÷ 1,000 = 3.088 V. The worksheet displays 3.09 V and 2.57% (3.088 ÷ 120 × 100). This arithmetic does not establish whether the conductor is suitable for the installation.

Interpreting the estimate

Use the result as a planning value and keep input precision consistent with the measurements or source data you have. Small displayed differences can come from final-place rounding; intermediate values are not rounded.

Assumptions and limits

This worksheet does not choose wire size, determine ampacity, or establish electrical-code compliance. Obtain resistance from current manufacturer data and have electrical work designed and checked for the applicable installation. To plan where cable runs through wall framing, see the stud spacing calculator; for the room or home dimensions behind a load estimate, use the square footage calculator; and for elevated installation work, review the ladder safety calculator.

Empty or invalid inputs, prohibited negatives, zero denominators, impossible relationships, and unsupported options do not produce a potentially misleading numeric result.

Evaluate a candidate without claiming a full design

Keep system voltage, current, and one-way length fixed while comparing candidate conductor resistances. This isolates the voltage-drop effect of resistance. Retain the entered resistance basis with the result; a voltage-drop calculation does not establish conductor ampacity or compliance with a wiring standard.

Sources

Compare Two-Conductor Voltage Drop Calculator with related tools

All comparisons →
Electric Current vs Voltage DropCompare current-unit conversion with a two-conductor voltage-drop worksheet using known resistance. Neither tool selects a conductor size.Voltage Drop vs Stud SpacingCompare the two-conductor voltage-drop worksheet with the wall stud spacing calculator's framing count for planning wiring runs through framed walls.

Frequently asked questions

How is voltage drop calculated?

For a two-conductor path, voltage drop is 2 times current times resistance times the one-way run length divided by 1,000, using the candidate-conductor resistance in ohms per 1,000 feet. Percentage drop divides that result by system voltage.

Does the calculator choose the wire size for me?

No. This worksheet does not choose wire size, determine ampacity, or establish electrical-code compliance. Resistance should come from current manufacturer data, and electrical work should be designed and checked for the applicable installation.

What inputs does the worksheet need?

Enter voltage, current, one-way run length, and candidate-conductor resistance in ohms per 1,000 feet. Empty or invalid inputs, prohibited negatives, zero denominators, impossible relationships, and unsupported options do not produce a misleading numeric result.

Sources

  • NFPA 70 National Electrical Code

    primary · Aug 10, 2026

    Supports: Electrical installation and conductor safety requirements that frame the worksheet's scope and the caveat that adopted codes control safety-critical sizing.

    — National Fire Protection Association (NFPA)

  • Southwire Voltage Drop Calculator

    secondary · Aug 10, 2026

    Supports: The two-conductor voltage-drop relationship (2 × current × resistance × one-way length ÷ 1,000) used by the worksheet, with resistance taken from conductor data.

    — Southwire

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Two-Conductor Voltage Drop Calculator updated at

Recorded calculation check

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