Wire size calculator: what size wire do I need for my amps?
6 AWG copper
55 A at 60 °C, Table E3705.1 · in aluminum, 4 AWG · for a 50 A circuit in NM cable
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3/8 or 10' 6".
6 AWG copper
55 A at 60 °C, Table E3705.1 · in aluminum, 4 AWG
Source: IRC 2021 Table E3705.1, Allowable Ampacities, with Sections E3705.4.1, E3705.4.2 and E3705.4.4 and Table E3705.5.3 (International Code Council), read November 3, 2026. Read the source
A 50 amp circuit in NM cable (Romex) needs 6 AWG copper, rated 55 amps in the 60 °C column of IRC 2021 Table E3705.1; in aluminum it is 4 AWG.
A worked example
A 70 amp feeder in aluminum THHN to a garage subpanel needs 2 AWG aluminum. At 70 A the terminals count at 60 °C (Section E3705.4.1), where 4 AWG aluminum carries 55 A and 3 AWG 65 A, so the first that reaches 70 is 2 AWG at 75 A. With equipment marked 75 °C it would be 3 AWG, at 75 A.
What size wire for a 30 amp breaker?
10 AWG copper: Table E3705.5.3 allows a 30 A breaker on 10 AWG and no larger, and 10 AWG carries 30 A at 60 °C. In aluminum, 8 AWG, which the same table caps at 30 A.
What size wire for a 60 amp breaker?
4 AWG copper in NM cable, 70 A at 60 °C; 6 AWG copper reaches only 55 A there. With THHN in conduit and equipment marked 75 °C, 6 AWG copper carries 65 A and is enough.
What size wire for 100 amps?
At 100 A or less the terminals count at 60 °C unless the equipment is marked otherwise: 1 AWG copper (110 A) or 1/0 aluminum (100 A). With 75 °C terminals, 3 AWG copper or 1 AWG aluminum, both 100 A.
What else it is called
Also searched as a wire gauge calculator, an electrical wire size calculator, what size wire for 50 amp, what size wire for a 30 amp breaker or an ampacity chart. AWG numbers run backwards: the smaller the number, the thicker the wire.
Ampacity chart
| Size | Copper 60 °C | Copper 75 °C | Copper 90 °C | Aluminum 60 °C | Aluminum 75 °C | Aluminum 90 °C |
|---|---|---|---|---|---|---|
| 14 AWG | 15 (15) | 20 (15) | 25 (15) | — | — | — |
| 12 AWG | 20 (20) | 25 (20) | 30 (20) | 15 (15) | 20 (15) | 25 (15) |
| 10 AWG | 30 (30) | 35 (30) | 40 (30) | 25 (25) | 30 (25) | 35 (25) |
| 8 AWG | 40 | 50 | 55 | 35 (30) | 40 (30) | 45 (30) |
| 6 AWG | 55 | 65 | 75 | 40 | 50 | 55 |
| 4 AWG | 70 | 85 | 95 | 55 | 65 | 75 |
| 3 AWG | 85 | 100 | 115 | 65 | 75 | 85 |
| 2 AWG | 95 | 115 | 130 | 75 | 90 | 100 |
| 1 AWG | 110 | 130 | 145 | 85 | 100 | 115 |
| 1/0 AWG | 125 | 150 | 170 | 100 | 120 | 135 |
| 2/0 AWG | 145 | 175 | 195 | 115 | 135 | 150 |
| 3/0 AWG | 165 | 200 | 225 | 130 | 155 | 175 |
| 4/0 AWG | 195 | 230 | 260 | 150 | 180 | 205 |
| 250 kcmil | 215 | 255 | 290 | 170 | 205 | 230 |
| 300 kcmil | 240 | 285 | 320 | 195 | 230 | 260 |
| 350 kcmil | 260 | 310 | 350 | 210 | 250 | 280 |
| 400 kcmil | 280 | 335 | 380 | 225 | 270 | 305 |
| 500 kcmil | 320 | 380 | 430 | 260 | 310 | 350 |
Allowable ampacity in amps, IRC 2021 Table E3705.1, not more than three current-carrying conductors at 30 °C (86 °F). In brackets, the largest breaker Table E3705.5.3 allows on 14, 12 and 10 AWG copper and 12, 10 and 8 AWG aluminum. NM cable stays in the 60 °C column (Section E3705.4.4), and so do circuits of 100 A or less unless the equipment is marked otherwise (E3705.4.1).
Where the numbers come from
- IRC 2021 Table E3705.1: allowable ampacity of copper and aluminum conductors 14 AWG to 900 kcmil at 60 °C (Types TW, UF), 75 °C (RHW, THHW, THW, THWN, USE, XHHW) and 90 °C (RHW-2, THHN, THHW, THW-2, THWN-2, XHHW, XHHW-2, USE-2). Read November 3, 2026, in the Colorado adoption, and checked the same day in the Virginia adoption. IRC 2021 Chapter 37
- Section E3705.4.4: “The allowable ampacity of Types NM and NMC cable shall not exceed that of 60°C (140°F) rated conductors.” Section E3705.4.1: terminals of circuits rated 100 amperes or less use the 60 °C ampacity unless the equipment is marked otherwise; E3705.4.2: over 100 amperes, 75 °C. IRC 2021 Chapter 37
- Table E3705.5.3: the largest breaker on 14, 12 and 10 AWG copper is 15, 20 and 30 A, and on 12, 10 and 8 AWG aluminum 15, 25 and 30 A. The column used is the lower of the wire's rating and the terminals'; the size is the smallest that reaches the amps in that column without passing its breaker limit.
The ampacities are for up to three current-carrying conductors at 30 °C (86 °F). Hotter spaces and bundles of more conductors take the factors of Sections E3705.2 and E3705.3, voltage drop over long runs needs conductor resistances the IRC does not print, and dwelling services sized by the 83 percent rule of Table E3603.1 are not in this calculator.
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