In U.S. homes, Romex® (NM-B) is sold in gauges such as 14/2, 12/2, 10/2, and larger, with the gauge chosen to match the circuit amperage and code.
Asking “what gauge is Romex” sounds simple, yet the right answer depends on the job, the breaker, and the rules your project must follow. Romex® is a brand name for copper nonmetallic-sheathed cable, labeled NM-B. You’ll find it on shelves from 14 AWG up through 6 AWG and beyond, in two-conductor and three-conductor versions with a bare ground. This guide lays out the sizes you’ll actually use, how they pair with breakers, and where each size fits.
Common Romex® Gauges And Everyday Uses
The table below lines up the go-to NM-B sizes for U.S. residential work. It assumes copper conductors and standard conditions.
| Gauge & Cable | Typical Breaker | Common Uses |
|---|---|---|
| 14/2 with ground | 15 A | Lighting circuits, small rooms on 15 A general circuits |
| 14/3 with ground | 15 A | 3-way lighting, split-wired receptacles needing a neutral |
| 12/2 with ground | 20 A | Kitchen small-appliance circuits, garage, laundry |
| 12/3 with ground | 20 A | Two-pole smart switches, multi-wire branch circuits |
| 10/2 with ground | 30 A | 240 V water heaters, baseboard heat (no neutral load) |
| 10/3 with ground | 30 A | Dryers needing neutral, older cooktops on 30 A |
| 8/3 with ground | 40–45 A | Some cooktops, medium ranges per nameplate |
| 6/3 with ground | 50 A | Full-size electric ranges, EVSE that calls for 50 A |
Romex Wire Gauge In The USA: Sizing Basics
American Wire Gauge (AWG) counts down as wires grow thicker. So 12 AWG is larger than 14 AWG, and 10 AWG is larger than 12 AWG. In NM-B cable, the print on the jacket tells you the gauge and the conductor count: like “12/2 with ground” means two insulated 12-gauge conductors plus a bare equipment ground. “12/3 with ground” adds a red insulated conductor, handy when a neutral or a second hot is required.
Romex® is NM-B, which uses 90 °C rated insulation inside the sheath, yet branch-circuit sizing for NM-B is based on the 60 °C column, then adjusted if needed for bundling or heat. That pairing is why most homes land on a few clear rules: 14 copper pairs with a 15-amp breaker, 12 copper pairs with 20 A, and 10 copper pairs with 30 A. Larger gauges step up from there based on the appliance nameplate and the overcurrent device.
Breaker Size And Ampacity Rules That Matter
For small copper conductors, breaker limits are straightforward: 14 AWG is protected at 15 A, 12 AWG at 20 A, and 10 AWG at 30 A. Those caps apply to NM-B branch circuits unless a specific equipment article tells you otherwise. The 90 °C conductor rating inside NM-B is there so you can apply adjustment and correction math, but the end result still can’t exceed the 60 °C ampacity when used as NM-B.
Translation: pick the breaker by the small-conductor limits, then check any correction for hot attics or bundles, and finally confirm the equipment’s nameplate. That simple flow keeps you inside the rules and matches real-world practice.
Decoding The Jacket Print And Colors
Your fastest check is the ink on the jacket. A typical line reads “NM-B 12/2 with ground 600 V.” That string gives you the cable type (NM-B), the gauge (12), how many insulated conductors (2 or 3), and whether a bare ground is present. Many makers also use color-coded jackets that match common sizes—white for 14, yellow for 12, orange for 10, and black for 8 or 6. Color isn’t a rule and older stock may vary, so always read the print.
Where Each Size Fits Best
Lighting And General-Use Rooms
Many homes wire bedroom and living-area lighting on 15-amp circuits using 14/2 NM-B. Where a 3-way switch is planned, 14/3 is the tidy choice. Some builders upgrade general-use receptacles to 20 A with 12/2 for a bit more headroom. Either way, the breaker must match the copper gauge.
Kitchens, Laundry, And Garages
Countertop receptacles and laundry outlets commonly use 12/2 on 20-amp circuits. That matches small-appliance demand and tool loads. Garages frequently follow the same pattern, and many local rules add GFCI and AFCI devices as required by the edition in force.
240-Volt Appliances
Loads that don’t need a neutral—such as many tank water heaters or straight-resistance baseboard heaters—often land on 10/2 NM-B with a 30-amp two-pole breaker. Appliances that do need a neutral, like most modern electric dryers and full ranges, call for /3 cable so the neutral and the two hots travel together with the equipment ground. Typical pairs are 10/3 on 30 A for a dryer and 6/3 on 50 A for a range, though the nameplate rules the day.
When To Choose /3 Instead Of /2
Think about the conductors you need at the device. /2 gives you one hot and one neutral (or two hots for a straight 240 V load) plus ground. /3 adds a red conductor. That extra insulated wire lets you carry a neutral for a 120/240 V appliance, run a multi-wire branch circuit with a tied two-pole breaker, or feed a smart control that needs a second switched leg. If a future upgrade is likely, pulling /3 upfront can save a second trip.
Derating: Heat, Bundling, And Tight Openings
Attic spaces get hot, and many cables stuffed through one hole act like a bundle. Both situations reduce how much current a conductor can carry. With NM-B, you can start from the 90 °C conductor rating for the math, apply the required correction or adjustment, and then confirm the number still meets the 60 °C limit for NM-B. Spread the holes through studs, keep air around the cable, and avoid burying long stretches in insulation when you have room to route elsewhere.
Voltage Drop And Long Runs
Every copper run drops a bit of voltage as length grows. Keep branch-circuit drop near three percent. On long hallways or detached spaces, upsizing the cable one gauge tames nuisance dimming and heat at connections. A 20-amp circuit that stretches a long way might jump from 12 AWG to 10 AWG; a long 15-amp circuit might jump from 14 AWG to 12 AWG. The breaker stays the same; you’re only reducing drop.
| Circuit | Typical One-Way Run | Upsize To |
|---|---|---|
| 15 A lighting on 14 AWG | Over ~75–100 ft | 12 AWG copper |
| 20 A receptacles on 12 AWG | Over ~75–100 ft | 10 AWG copper |
| 30 A dryer on 10 AWG | Over ~100–125 ft | 8 AWG copper |
Places NM-B Isn’t Allowed
NM-B is for dry, indoor spaces. It can’t go outdoors without a raceway, into wet or damp locations, into masonry that can get wet, or where the cable would be exposed to damage. In garages with open walls, in unfinished basements, or in outbuildings, use listed protection or a wiring method that’s rated for the conditions. For underground runs, choose UF-B cable or conduit with individual wet-rated conductors.
Working With Cable Safely
Good layout and neat routing go a long way. Support NM-B at the spacing the rules call for and within the distance from boxes. Use listed staples sized for the jacket. Keep bends gentle; avoid kinks. Strip the outer sheath cleanly so the paper wrap and conductors aren’t nicked. At device boxes, plan the pigtails, leave enough free conductor for the device, and check the box-fill number so you don’t cram too much in a small box.
Troubleshooting Existing Runs
Upgrading a room and not sure what you’ve got? Read the jacket. You’ll see the gauge, the conductor count, and the NM-B marking. Compare that to the breaker size. If a 20-amp breaker feeds 14-gauge NM-B, that pairing needs correction. On a dryer or range, check whether the cable is /3 with a neutral or /2 without. Look for shared neutrals on two hots only when a two-pole handle-tied breaker is in place. Fix loose terminations and replace worn cable clamps as you go.
How To Read A Reel And Buy The Right Cable
Store shelves list NM-B by gauge and length. Before you buy, match three things: breaker size, load needs, and conductor count. Then check any special notes on the appliance label and measure your path with some slack for routing. Most reels are marked in feet as you pull, which helps avoid waste and splices.
Quick Buying Checklist
- Match 15 A with 14/2, 20 A with 12/2, 30 A with 10/2 or 10/3 as needed.
- Pick /3 when a neutral or second hot is required.
- Read the jacket print; don’t rely on jacket color alone.
- Plan for voltage drop on long runs by upsizing one gauge.
- Use GFCI/AFCI where the rules call for them.
- Choose a wiring method rated for wet, damp, or exposed spots.
Real-World Examples
Small Bedroom Remodel
New lighting on a 15-amp breaker? Pull 14/2 NM-B from the panel to the light box. Add a 3-way? Pull 14/3 between the two switch boxes. Keep stapling and box-fill rules in mind and you’re set.
Kitchen Countertop Circuit
A pair of 20-amp small-appliance circuits is the go-to setup. Run 12/2 NM-B from a two-pole or two separate 20-amp breakers (handle-tied if run as a multi-wire branch circuit using 12/3). Keep the neutral continuous, share it only on a two-pole device, and use GFCI/AFCI protection as required.
New Electric Dryer
Most dryers list 30 A at 120/240 V and need a neutral. That points to 10/3 NM-B on a 30-amp two-pole breaker. If the label lists a 240-V only design without a neutral, 10/2 may be fine. Always wire to the nameplate.
Why People Say “Romex”
Romex® is a well-known brand for NM-B copper cable. It’s a trade name, not a wiring method by itself. The method is “NM-B” as defined by the wiring rules, and several manufacturers make it. Look for the NM-B marking first; the brand is secondary.
What About Aluminum?
Standard NM-B uses copper. Aluminum building wire shows up in larger feeder cables, service-entrance cable, and certain branch-circuit types, but not as typical NM-B for outlets or lighting. If you’re pricing large feeders, you’ll see different cable types and a separate set of sizing rules.
Simple Sizing Steps You Can Trust
- Choose the breaker size based on the load and the small-conductor limits.
- Pick the NM-B gauge that matches the breaker.
- Decide /2 or /3 based on neutral needs and device features.
- Check the appliance label and any adjustment for heat or bundling.
- Upsize for long runs to keep voltage drop in check.
Sources You Can Check
Manufacturer pages clearly describe NM-B construction, markings, and typical uses. You can also read the electrical code in a free viewer. Both links below open in a new tab: