Reading Wire Markings and AWG Sizes

A typical print string reads like this: THHN 12 AWG 600V 90°C (UL). Reading left to right: THHN is the wire type (thermoplastic, high heat-resistant, nylon-coated); 12 AWG is the size; 600V is the voltage rating; 90°C is the temperature rating; (UL) is the listing agency. Sheathed cables add conductor count — 12/2 means 12 AWG, two conductors plus ground. Photograph the clearest few inches; even a fragment like “AWG” plus a number is usually enough to identify the wire.

AWG stands for American Wire Gauge — the standard sizing system for wire in North America. The rule that trips everyone up: the smaller the number, the bigger the wire. 14 AWG is thin branch-circuit wire; 4/0 (pronounced “four-aught”) is a thick feeder cable. Gauge matters to sellers because bigger wire carries more copper per foot — a foot of 2 AWG holds far more copper than a foot of 18 AWG. Sizes run from fine 40 AWG magnet wire up through 1000 kcmil industrial cable; most scrap wire falls between 24 and 4/0 AWG.

Constructions vary by manufacturer and era — these are the gauges you will typically encounter:

• Home branch circuits: 14 and 12 AWG
• Large appliances, A/C, dryers: 10, 8, 6 AWG
• Service runs and feeders: 4 AWG through 4/0 and larger
• Phone and network cable: 24 AWG (Cat5/5e), 23 AWG (Cat6), 22 AWG (older phone)
• Thermostat and alarm wire: 18–22 AWG
• Automotive and battery cable: 18 through 4/0 AWG
• Welding and DLO cable: 6 AWG through 4/0 and larger

Romex-style NM-B cable follows an industry color convention worth knowing: white sheath is typically 14 AWG, yellow is 12 AWG, orange is 10 AWG, and black is commonly 8 or 6 AWG. It is a convention, not a code requirement — always confirm against the printed markings — but it lets an experienced eye gauge a coil at a glance.

Photograph what you have — the wire, any jacket markings, and the overall quantity — and send it to Ironcrest for today’s offer. We buy nationally and coordinate pickup from your site.

Sell your copper to Ironcrest →  |  Call or text 312-880-8174  |  Send photos →

See also: What type of copper wire do I have?  |  Building wire guide  |  Copper wire grades guide (canonical)

What does AWG stand for?

American Wire Gauge — the standard system for sizing wire in North America. Remember the one rule: a smaller AWG number means a bigger wire.

What do the letters THHN mean?

Thermoplastic, High heat-resistant, Nylon-coated — a single-conductor building wire commonly pulled through conduit in commercial and industrial work.

What does “12/2” mean on Romex?

12 AWG conductors, two of them — plus a bare ground wire. So “12/2 with ground” is three wires inside the sheath: black, white, and bare copper.

How do I measure wire gauge if there are no markings?

Strip a short section, measure the bare copper diameter with calipers, and compare it to an AWG chart — or photograph the wire next to a ruler and send it to a buyer. Gauge identification from a photo is routine.

Is bigger-gauge wire worth more?

Per foot, generally yes — larger wire carries more copper per foot, and heavy insulated wire grades higher than thin communications wire. Condition, type, and quantity matter too, which is why photos get you the real answer.