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

By CalcMesh Editorial · Reviewed against primary-source formulas

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.

Wire Sizing, Code and Physics

The National Electrical Code 2023 (NFPA 70) Table 310.16 sets ampacity: 14 AWG copper carries 15 A, 12 AWG = 20 A, 10 AWG = 30 A, 8 AWG = 40-50 A depending on insulation type. These are the legal minimums for residential branch circuits — arc-fault and ground-fault protection are additionally required on most circuits since 2020. Undersizing conductors is the #1 finding in insurance electrical-fire investigations.

Voltage drop compounds ampacity considerations. The NEC recommends total voltage drop ≤5% (branch + feeder), and industry practice holds branch circuits to ≤3%. For a 100-foot run at 20 A and 120 V, 12 AWG drops 4.3 V (3.6%) — marginal but acceptable; the same run at 240 V drops only 1.8% because higher voltage halves current for the same power. For longer runs, 10 AWG reduces drop to 2.7 V (2.3%), usually the better choice.

EV charging has surfaced residential-wiring limits. A Level 2 charger at 40 A continuous requires a 50 A circuit (NEC 625.42 mandates 125% ampacity), which means 6 AWG copper or 4 AWG aluminum. The Edison Electric Institute estimates 70% of single-family homes lack adequate 200 A service for both an EV charger and electrification (heat pump, induction range) — upgrade costs average $2,500-$7,500 per home per the 2022 Brattle Group study.

Sources: NEC 2023 NFPA 70, Brattle Group 2022 electrification study, EEI

Methodology & Assumptions

This calculator implements standard formulas drawn from primary-source authorities. Values are point-in-time estimates; consult a licensed professional for high-stakes decisions. See the per-input definitions and source citations below.

How this works

Computations are deterministic and run client-side — no inputs leave your browser. Formulas are derived from standard published formulas for the calculator's domain (mortgage, taxes, energy, conversions, etc.). When the underlying agency publishes updated rates or thresholds we refresh defaults and update the page's lastmod timestamp.

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.