Engineering calculator

Wire Gauge Calculator, AWG Size by Current, Distance & Voltage Drop

Find the correct AWG wire gauge for your circuit based on current load, run distance, and maximum voltage drop. Covers copper and aluminum conductors.

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A
ft

Distance from panel to load (not round-trip)

%

NEC recommends 3% for branch circuits

Recommended AWG

–

Minimum wire size

Max Ampacity

–

NEC rated capacity

Actual Voltage Drop

–

At recommended gauge

Voltage Drop %

–

Of system voltage

Wire Resistance

–

Round-trip total

Voltage at Load

–

After drop

How CalcMesh sizes wire gauge

American Wire Gauge (AWG) sizing balances current, distance and acceptable voltage drop. According to the National Electrical Code published by the National Fire Protection Association, conductor ampacity and a voltage drop under about 3% are the usual design limits.

We recommend a gauge from your current, length and voltage, but local code and conditions govern the final choice; the ampacity references we use are listed in our methodology.

Wire Sizing Guide

NEC Wire Sizing Rules

The National Electrical Code requires wire to be sized for both ampacity (current-carrying capacity) and voltage drop. The wire must satisfy both requirements, always use the larger of the two sizes.

  • Ampacity: Wire must be rated to safely carry the circuit current without overheating
  • Voltage drop: NEC recommends max 3% drop for branch circuits, 5% total including feeder

Common Household Circuits

Circuit Amps Typical AWG
Lighting 15A 14 AWG
General outlets 20A 12 AWG
Dryer / AC unit 30A 10 AWG
Range / Oven 40-50A 6-8 AWG
Service entrance 100-200A 1-4/0 AWG

Safety Considerations

  • Always size wire for the breaker rating, not the expected load
  • Derate ampacity for conduit fill, ambient temperature, and bundling
  • Use THHN/THWN rated wire for most residential applications
  • Longer runs almost always need upsizing for voltage drop

Copper vs Aluminum

This calculator uses copper wire values. For aluminum wire, go up 2 AWG sizes (e.g., if copper calls for 10 AWG, use 8 AWG aluminum). Aluminum requires anti-oxidant compound and rated connectors.

Disclaimer: Always consult a licensed electrician and follow local electrical codes. This calculator provides estimates for planning purposes only.

Worked example, 20 A @ 100 ft, 120 V, 3% drop

Labelled copper branch-circuit sizing check (illustrative; local NEC/AHJ governs):

  • I = 20 A, one-way = 100 ft, V = 120 V, allow 3% → max drop 3.6 V.
  • Ampacity alone often points to 12 AWG copper for 20 A; long run may force a larger gauge to hold drop.
  • Round-trip length = 2×100 = 200 ft of conductor in the resistance budget.
  • Always take the stricter of ampacity vs voltage-drop size; aluminum needs roughly two AWG sizes larger.

After you run the numbers

What to do with the results

  • Satisfy both ampacity and voltage-drop, use the larger required AWG.
  • Distance is one-way panel→load; resistance uses the round-trip path.
  • NEC 3%/5% figures are design recommendations, your AHJ and equipment limits can be tighter.
  • This page does not replace a licensed electrician’s load calculation or permit set.

Methodology & Assumptions

This circuit tool rearranges textbook electrical identities (Ohm, power, divider) on the values you enter. Component tolerances are not modelled—treat outputs as design starts.

How this circuit node runs

Ohm/power/divider tools rearrange textbook electrical identities. Real components carry tolerances the page does not invent. Published domain formulas govern the identities; when an agency updates rates or thresholds we refresh defaults and the page lastmod.

Frequently Asked Questions

Why does wire gauge matter?
Using wire that is too small for the current it carries creates excessive resistance, which causes voltage drop and heat buildup. Voltage drop reduces the performance of connected equipment (dim lights, slow motors), while excessive heat can melt insulation and cause fires. The National Electrical Code (NEC) specifies minimum wire sizes for safety.
What is acceptable voltage drop?
The NEC recommends no more than 3% voltage drop for branch circuits and 5% total for feeders plus branch circuits combined. For sensitive electronics, 2% or less is preferred. Long runs of wire (like to a detached garage or well pump) are especially prone to voltage drop and may require larger wire than the ampacity alone suggests.
What is the difference between copper and aluminum wire?
Copper has about 60% better conductivity than aluminum, so aluminum wire must be larger (typically 2 AWG sizes up) to carry the same current. Copper is more commonly used in residential wiring due to its better conductivity and easier termination. Aluminum is common in service entrance cables and utility lines because it is lighter and cheaper for large gauges.
What does AWG stand for?
AWG stands for American Wire Gauge, the standard system for measuring wire diameter in North America. Counter-intuitively, smaller numbers mean thicker wire. AWG 14 is common for 15-amp household lighting circuits, AWG 12 for 20-amp outlets, and AWG 10 for 30-amp dryer circuits. For wires thicker than 1 AWG, the system switches to 1/0 (one-ought), 2/0, 3/0, and 4/0.

This page identifies the inputs, method, and limitations behind its estimates. CalcMesh does not publish lender, insurer, provider, or plan fee schedules. Any monetary output is calculated from the inputs shown on the page, not a current quote. Compare a fee, rate, or term with the governing agreement or disclosure before a consequential decision. Calculator outputs are not professional advice. Circuit identities here rearrange the volts, amps, and resistances you enter—no lab certificate is implied. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.

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Inputs, defaults, and authoritative sources
Input Default Source / authority
All inputs Domain-typical defaults Editorial methodology, CalcMesh 2026