12/2 Romex Wire: The Complete Guide
12/2 Romex is the single most commonly used electrical cable in American residential construction. If you are wiring a kitchen, bathroom, garage, or any room that requires 20-amp circuits, 12/2 NM-B (the technical name for what most people call “Romex”) is the cable you need. Here is everything you need to know about 12/2 Romex: what the numbers mean, where to use it, what it costs, and how to buy it in the right quantity for your project.
What the Numbers Mean
The designation “12/2” tells you exactly what is inside the cable. The first number (12) is the wire gauge in American Wire Gauge (AWG). 12 AWG copper conductors are rated to carry a maximum of 20 amps safely. The second number (2) indicates that there are two insulated current-carrying conductors inside the cable sheath: one black (hot) and one white (neutral). In addition to the two insulated conductors, 12/2 NM-B always includes a bare copper ground wire, so the cable actually contains three wires total despite the “2” designation.
NM-B Rating
The “NM-B” designation stands for Non-Metallic sheathed cable, Type B. “Non-metallic” refers to the outer jacket material (PVC or similar thermoplastic), which distinguishes it from metal-clad (MC) cable that has an aluminum or steel armor jacket. The “B” rating indicates a 90-degree Celsius temperature rating on the individual conductor insulation, which is the current standard for all modern NM cable. NM-B is rated for dry indoor locations only. It is not rated for wet locations, outdoor exposure, direct burial, or installation in conduit in wet areas.
Where 12/2 Romex Is Used
Required by Code (20-Amp Circuits)
The National Electrical Code (NEC) requires 20-amp circuits with 12 AWG wire for kitchen countertop receptacles (at least two separate 20-amp circuits required), bathroom receptacles (dedicated 20-amp circuit required), garage receptacles, outdoor receptacles, laundry room receptacles for the washing machine, and dishwasher and garbage disposal circuits. These circuits must be 20-amp per code, which means 12 AWG is the minimum wire size. Using 14 AWG (which is rated for only 15 amps) on these circuits is a code violation.
Common Uses (20-Amp General Purpose)
Beyond the code-required applications, 12/2 Romex is used for general-purpose outlet circuits where the homeowner or electrician prefers the higher capacity of a 20-amp circuit, dedicated circuits for individual high-draw devices (space heaters, window AC units, shop tools), basement and workshop outlet circuits, and any branch circuit protected by a 20-amp breaker.
Where NOT to Use 12/2 Romex
Do not use NM-B cable outdoors or in any wet or damp location (use UF-B rated cable instead). Do not use NM-B in commercial construction where codes typically require conduit or MC cable. Do not use NM-B in exposed locations where it could be subject to physical damage (use MC cable or conduit instead). Do not bury NM-B underground even in conduit in wet areas (use UF-B for direct burial).
12/2 vs 14/2: When to Use Which
12/2 Romex is for 20-amp circuits. 14/2 Romex is for 15-amp circuits. The practical decision is straightforward: if the circuit is protected by a 20-amp breaker or if code requires a 20-amp circuit (kitchen, bathroom, garage, outdoor, laundry), use 12/2. If the circuit is protected by a 15-amp breaker and serves general lighting or low-demand outlets, 14/2 is acceptable. Many electricians prefer to wire entire homes with 12/2 for consistency and the flexibility to upgrade any circuit to 20 amps in the future. The additional cost of 12/2 over 14/2 is modest on a per-circuit basis.
12/2 vs 12/3: When to Use 12/3
12/3 Romex contains three insulated conductors (black, white, and red) plus a bare ground. The third conductor allows the cable to serve two separate circuits sharing a neutral (a multi-wire branch circuit), a circuit requiring a switched and unswitched conductor (such as a switched outlet or a fan/light combination), or a 240-volt circuit that also provides 120 volts (such as certain appliance circuits). For standard 120-volt, single-circuit applications, 12/2 is the correct choice. Use 12/3 only when the circuit design specifically requires the third conductor.
Available Lengths and Packaging
12/2 NM-B is sold in standard spool sizes of 25-foot rolls (small projects and repairs), 50-foot rolls, 100-foot rolls, 250-foot spools (the most common contractor size), 500-foot spools, and 1,000-foot spools (for large projects and multi-home jobs). IB Lighting stocks 12/2 Romex in 250-foot, 500-foot, and 1,000-foot quantities from major manufacturers including Southwire. Larger spool sizes offer a lower cost per foot and reduce waste from partial spools on bigger projects.
Buying 12/2 Romex
IB Lighting ships 12/2 Romex NM-B cable nationwide with free freight insurance on every order. Bulk pricing is available for contractor and multi-spool orders. Browse our electrical wire and cable selection to see current availability and pricing, or call (800) 674-9019 for volume quotes and custom lengths. We also carry the full range of Southwire products at our Southwire brand page.