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Ampacity lookup
Pick a wire size and insulation rating — get the allowable amps plus the max breaker.
REFERENCE TABLE · CONSTRUCTION · ELECTRICAL
Wire Gauge Ampacity Chart (NEC Table 310.16)
How many amps each copper wire size can safely carry — the numbers electricians actually look up, from NEC Table 310.16, with the two rules that trip up DIYers baked in. Rule one: the insulation’s temperature rating decides which column you read (THHN reads the 90°C column, but your breaker’s terminals usually cap you at 75°C). Rule two: 14, 12, and 10 AWG copper can never take more than a 15, 20, or 30-amp breaker — NEC 240.4(D) — even though the table lists higher ampacities. Below: the full printable chart, a breaker-to-wire finder, and three live lookups. At the defaults, 12 AWG THHN carries 30 amps but still maxes out at a 20-amp breaker.
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Breaker → wire finder
Know the breaker? Get the minimum copper wire size for it.
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Max breaker lookup
Pick a wire size — get the largest breaker NEC allows on it.
The full copper ampacity table
NEC 2023 Table 310.16, copper conductors — up to three current-carrying conductors at 30°C (86°F) ambient. Print this for the job site:
| Wire size | 60°C | 75°C | 90°C | Max breaker |
|---|---|---|---|---|
| 14 AWG | 15 A | 20 A | 25 A | 15 A |
| 12 AWG | 20 A | 25 A | 30 A | 20 A |
| 10 AWG | 30 A | 35 A | 40 A | 30 A |
| 8 AWG | 40 A | 50 A | 55 A | 50 A |
| 6 AWG | 55 A | 65 A | 75 A | 65 A |
| 4 AWG | 70 A | 85 A | 95 A | 85 A |
| 3 AWG | 85 A | 100 A | 115 A | 100 A |
| 2 AWG | 95 A | 115 A | 130 A | 115 A |
| 1 AWG | 110 A | 130 A | 145 A | 130 A |
| 1/0 AWG | 125 A | 150 A | 170 A | 150 A |
| 2/0 AWG | 145 A | 175 A | 195 A | 175 A |
| 3/0 AWG | 165 A | 200 A | 225 A | 200 A |
| 4/0 AWG | 195 A | 230 A | 260 A | 230 A |
How to read it: find your wire size, then read the column matching the wire’s insulation rating — but never above what the breaker and device terminals are rated for (NEC 110.14(C); most residential gear is 75°C). The Max breaker column is the overcurrent limit: for 14/12/10 AWG that’s the 240.4(D) small-conductor cap, for 8 AWG and up it’s the termination-limited ampacity. Long runs need upsizing for voltage drop — ampacity is heat, not distance.
Breaker → wire quick chart
| Breaker | NM-B (Romex) | THHN in conduit |
|---|---|---|
| 15 A | 14 AWG | 14 AWG |
| 20 A | 12 AWG | 12 AWG |
| 30 A | 10 AWG | 10 AWG |
| 40 A | 8 AWG | 8 AWG |
| 50 A | 6 AWG | 8 AWG |
| 60 A | 4 AWG | 6 AWG |
| 100 A | 1 AWG | 3 AWG |
Output · formula · meaning
| Output | Formula | What it means |
|---|---|---|
| Ampacity | Table 310.16 lookup (size × temp column) | The max continuous current: 30 A for 12 AWG at 90°C. |
| Max breaker | min(ampacity, 240.4(D) cap) | The largest overcurrent device allowed: 20 A on 12 AWG. |
| Min wire for breaker | smallest AWG with ampacity ≥ breaker | A 30 A breaker needs at least 10 AWG copper. |
Who uses this
- DIYers wiring a circuit: confirming the wire matches the breaker before buying the spool.
- Apprentice electricians: the Table 310.16 values and the 240.4(D) caps, drilled as lookups.
- Home inspectors & buyers: spotting an oversized breaker on a small wire — the classic panel red flag.
- Researchers & students: NEC table values are published code data — cite them with the block below.
Accuracy & limitations
Values are NEC 2023 Table 310.16 for copper at 30°C ambient with up to three current-carrying conductors — the starting point, not always the final answer. Hot attics, bundled cables, and continuous loads (over 3 hours) require derating that can drop a size. Aluminum runs about one size larger for the same amps. Local amendments may differ; your AHJ (authority having jurisdiction) has the last word. This is a reference, not a permit — when in doubt, hire a licensed electrician.
Cite this tableBright Side Kit. “Wire Gauge Ampacity Chart: NEC 310.16.” brightoolbox.com, 2026.
Bright Side Kit. "Wire Gauge Ampacity Chart: NEC 310.16." https://brightoolbox.com/wire-gauge-ampacity-chart/ Accessed October 23, 2026.Frequently asked questions
Why can’t I use a 30-amp breaker on 12 AWG THHN rated for 30 amps?
Because of NEC 240.4(D), the small-conductor rule: overcurrent protection on 14, 12, and 10 AWG copper is capped at 15, 20, and 30 amps respectively, regardless of what the 90°C column says. The table lists the wire’s heat capacity (30 A for 12 AWG at 90°C); the rule limits the breaker. The lookup above shows both numbers so the distinction is never missed.
What do the 60°C, 75°C, and 90°C columns mean?
They match the wire’s insulation temperature rating: TW/UF jackets read the 60°C column, THW/XHHW the 75°C column, THHN/THWN-2 the 90°C column. Hotter-rated insulation lets the same copper carry more current. But NEC 110.14(C) adds the catch: you can’t use a column hotter than your breaker and device terminals are rated for — and most residential gear is 75°C, so the 90°C column is usually just a starting point for derating math.
Can I just use the 90°C column for everything?
Only if every termination is 90°C-rated too — the wire, the breaker lugs, and the device. In homes, that’s rare: NM-B (Romex) is a 60°C wiring method, and standard breakers and receptacles are 75°C. The honest rule: read the column your weakest component allows. The 90°C column still matters — it’s the starting point when derating for hot attics or bundled cables.
What about aluminum wire?
Aluminum carries less current per size — roughly one AWG size larger than copper for the same amps (12 AWG aluminum ≈ 14 AWG copper at 15 A). This page’s chart and lookups are copper only; aluminum has its own Table 310.16 columns and needs antioxidant paste and CO/ALR-rated devices at terminations. Size aluminum separately.
Does wire length change the ampacity?
No \u2014 but it changes the wire you should buy. Ampacity is about heat: how much current the wire can carry without overheating its insulation. Length causes voltage drop, a separate problem — a long run at full ampacity can still starve the load of volts. Rule of thumb: runs over ~100 feet at 120 V often need one size up for voltage drop even when the ampacity table says the smaller wire is fine.
Is this chart the final answer for my project?
It’s the starting point. Table 310.16 assumes 30°C ambient and at most three current-carrying conductors. Hot attics, conduit stuffed with circuits, and continuous loads (3+ hours, like EV chargers) all require derating that can cost you a wire size. Local code amendments can differ, and your inspector (the AHJ) has the last word. Treat this as the reference the pros start from — not a substitute for one.