What size wire do I need for a 20-amp circuit?

A 20-amp circuit requires minimum 12 AWG copper wire (12/2 NM-B for standard circuits or 12/3 for switch legs and 3-way switches). Using 14 AWG on a 20-amp breaker is a code violation. The number before the slash indicates gauge, and the number after indicates the count of current-carrying conductors.

Can I use 14 gauge wire for outlets?

Yes, 14 AWG wire is acceptable for outlets on 15-amp circuits per NEC. However, many jurisdictions and experienced electricians prefer 12 AWG minimum for all outlet circuits because it provides more capacity and future flexibility at a modest cost increase. Kitchen, bathroom, and garage outlets require 12 AWG on 20-amp circuits.

What is the difference between NM-B and UF-B wire?

NM-B (Romex) has a paper-wrapped, plastic-sheathed construction for dry indoor locations only. UF-B has solid waterproof insulation molded around the conductors, rated for underground burial, damp, and wet locations. UF-B can be used anywhere NM-B can, but NM-B cannot be used where UF-B is required.

Electrical

Electrical Wire Gauge Chart: Sizes, Types, and Amperage Ratings (2026)

Prepared by Lumberama's Building Materials Team

|Last updated June 23, 2026|Sources & methodology

Selecting the correct electrical wire gauge and type is critical for safety, code compliance, and preventing fire hazards. Wire that is too small for the circuit amperage overheats, while the wrong type in the wrong location violates code. This guide covers AWG sizing, common wire types, and the right wire for every residential circuit.

Key Takeaways

Selecting the correct electrical wire gauge and type is critical for safety, code compliance, and preventing fire hazards.
Wire that is too small for the circuit amperage overheats, while the wrong type in the wrong location violates code.
This guide covers AWG sizing, common wire types, and the right wire for every residential circuit.
Wire gauge must match the circuit breaker amperage: 14 AWG for 15-amp circuits, 12 AWG for 20-amp circuits, 10 AWG for 30-amp circuits, 8 AWG for 40-amp circuits, and 6 AWG for 50-amp circuits.
Choose NM-B for standard interior runs, UF-B for underground, and THHN in conduit for exposed locations.

Types Overview

NM-B (Romex) is the standard residential wire with plastic sheathing for dry indoor locations. UF-B wire has waterproof sheathing for underground and wet location use. THHN/THWN individual conductors run in conduit for exposed, outdoor, and commercial applications. MC (metal clad) cable has an armor jacket for commercial and exposed residential runs. Service entrance cable (SER/SEU) connects the meter to the main panel. Low-voltage wire (18-22 AWG) handles doorbells, thermostats, and landscape lighting.

Selection Criteria

Wire gauge must match the circuit breaker amperage: 14 AWG for 15-amp circuits, 12 AWG for 20-amp circuits, 10 AWG for 30-amp circuits, 8 AWG for 40-amp circuits, and 6 AWG for 50-amp circuits. Choose NM-B for standard interior runs, UF-B for underground, and THHN in conduit for exposed locations. Copper is standard for branch circuits; aluminum is acceptable for service entrance and large feeder circuits with proper connections.

Installation Guide

Run NM-B cable through drilled holes in framing, centered in studs to avoid drywall screws. Secure cable with staples within 12 inches of every box and every 4.5 feet along the run. Leave 6-8 inches of wire extending from each box. Strip sheathing carefully without nicking conductor insulation. Make proper connections using wire nuts or push-in connectors rated for the conductor size. Install nail plates where cable passes through framing less than 1-1/4 inches from the face.

Code Requirements

NEC Article 334 governs NM-B cable installation. 14 AWG wire maximum on 15-amp circuits, 12 AWG on 20-amp circuits — many jurisdictions require 12 AWG minimum for all branch circuits. Kitchen, bathroom, garage, and outdoor receptacles require 20-amp circuits. Dedicated 20-amp circuits required for bathrooms, kitchen countertop receptacles, laundry, and garage. AFCI protection required for most living areas. GFCI protection for bathrooms, kitchens, garages, outdoors, and crawlspaces.

Cost Breakdown

14/2 NM-B (250 ft): $60-$90. 12/2 NM-B (250 ft): $80-$120. 10/2 NM-B (250 ft): $120-$180. 10/3 NM-B (for dryers, 125 ft): $120-$160. 6/3 NM-B (for ranges, 125 ft): $200-$300. UF-B 12/2 (250 ft): $100-$150. THHN 12 AWG (500 ft): $50-$80. Prices fluctuate with copper market conditions.

DIY vs Professional

Electrical work requires permits and inspection in most jurisdictions. Many areas allow homeowners to pull permits for their own residence. Basic circuit extensions and outlet additions are feasible for knowledgeable DIYers. Panel work, service upgrades, and new circuit installation should be performed by licensed electricians. Mistakes in electrical work create fire and shock hazards with potentially deadly consequences.

Common Mistakes to Avoid

Using 14 AWG wire on a 20-amp breaker is a code violation and fire hazard. Running NM-B cable in exposed outdoor locations where UF-B or conduit is required. Backstabbing receptacles instead of using screw terminals or proper push-in connectors leads to loose connections and arcing. Not installing nail plates on framing where cable is less than 1-1/4 inches from the face. Overfilling electrical boxes beyond the NEC fill calculation.

Frequently Asked Questions

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