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Wire Size Calculator

Audit voltage-drop arithmetic for one source-selected candidate conductor using documented impedance, path and units—without selecting AWG, ampacity, an allowable drop or code compliance.

Use this result well

Inputs that matter
One de-identified circuit calculation, an already selected candidate-conductor record, its named effective impedance source, paired length/impedance units, current, one-way length, path multiplier and source voltage
Output to expect
Source-preserving candidate voltage drop, percentage and load-side voltage arithmetic for that entered model only
How it works
Evaluate current × one-way length × documented path multiplier × candidate impedance per 1,000 units ÷ 1,000; do not select AWG, ampacity, an allowable drop, conductor, breaker or code verdict
  • Verify conductor material/construction, impedance temperature and AC/DC conditions, route length, circuit/phase model and calculation current against the responsible design and manufacturer data.
  • Final selection must also reconcile load calculation, continuous loads, terminations, insulation/listing, ambient and bundling corrections, fault current, grounding, overcurrent protection, adopted code and AHJ requirements.

Choose your path

Built around the job you need to finish

Audit voltage-drop arithmetic for one source-selected candidate conductor without presenting the result as ampacity, an allowable drop, a recommended wire size or code compliance.

Electrical designer checking one candidate

Reproduce a calculation without a generic ampacity table silently choosing copper AWG.

Name the candidate and impedance sources, copy the circuit model and inspect voltage/drop arithmetic.

Can trace the candidate while final conductor selection remains in the complete design.

Plan reviewer checking assumptions

See whether length, path multiplier, impedance conditions and voltage came from the submitted calculation.

Inspect source cards, paired units and each entered value rather than a bare AWG recommendation.

No ampacity, 3% pass/fail, breaker or approval is inferred.

Apprentice comparing circuit models

Learn why a 2× path or another documented phase multiplier cannot be guessed from three generic inputs.

Run separate foot and metre education records with explicit candidate data and compare steps.

Can explain the arithmetic and list the safety/design checks it omits.

Authoritative checks for this tool

Outputs and checklists are planning aids. Review the linked current authorities and the records, terms, instructions, and requirements that apply to your exact situation before a consequential decision.

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Reference & details

How it works

Start from a Selected Candidate

Material, construction, insulation, temperature and installation conditions affect usable data. This tool does not derive a candidate from current.

Candidate identity and impedance come from named sources

Keep the Circuit Model Explicit

The path multiplier represents the documented circuit/phase model. Two-wire, DC, single-phase and three-phase calculations cannot be collapsed into one hidden constant.

Drop = I × one-way length × entered path multiplier × impedance/1,000

Separate Arithmetic from Selection

The result receives no 3% pass/fail label. Ampacity, correction factors, protection, combined feeder/branch drop and local approval require the complete adopted design method.

Drop % = voltage drop ÷ entered source voltage × 100

Updated: August 2026

Example Scenarios

A named 8 AWG copper exercise candidate with 0.764 Ω/1,000 ft, 30 A, 50 ft and a documented 2× path gives 2.292 V drop. The tool does not recommend 8 AWG.

Select metres with Ω/km and copy the worksheet's path multiplier. Do not reuse an Ω/1,000 ft number without a validated conversion.

The tool preserves any finite load-side arithmetic and drop percentage without calling it compliant or selecting the next size. Return to the responsible design for candidate changes.

FAQ

No. The candidate must already come from a named responsible source. The tool only audits the entered candidate's voltage-drop model.

Resistance or impedance depends on material, size, construction, temperature and AC conditions. A source label makes those assumptions visible instead of embedding one copper table.

No. NFPA material distinguishes mandatory ampacity requirements from informational voltage-drop notes and feeder/branch context. The responsible design selects its applicable criterion.

It is the multiplier documented by the controlling circuit or phase model. Copy it; do not assume 2 or √3 without verifying the source calculation.

Verify load, continuous duty, ampacity, terminations, insulation/listing, ambient and bundling corrections, fault current, grounding, protection, adopted code and authority requirements.

About Wire Size Calculator

Check one candidate-conductor calculation without letting a generic form choose the wire. Name the candidate and impedance sources, copy the paired units, current, route length, path multiplier and voltage, then audit only that model's voltage-drop arithmetic.