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The amp rating of the breaker this wire will serve.
Size wire to the breaker's rating, not to the connected device's draw — the wire must be protected at the full breaker rating. If you are working from a load rather than a breaker, note that a CONTINUOUS load (three hours or more at full current, such as lighting or an EV charger) must be multiplied by 1.25 before it is used to size either the conductor or the breaker, per NEC 210.19(A)(1) and 210.20(A). Enter that increased figure, not the raw running current.
Minimum wire gauge
12 AWG
This is ampacity-only sizing — long runs may also need a thicker gauge to control voltage drop (see the Wire Gauge Voltage Drop Calculator).
- Ampacity of recommended gauge
- 20 A
They open the calculator with your figures already in it
Amperage to Wire Gauge Calculator: 12 AWG — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Standard copper conductor ampacity (NEC Table 310.16, 60°C column, typical for residential NM-B cable): 14 AWG=15A, 12 AWG=20A, 10 AWG=30A, 8 AWG=40A, 6 AWG=55A, 4 AWG=70A, 3 AWG=85A, 2 AWG=95A, 1 AWG=110A
- NEC 210.19(A)(1) and 210.20(A): a continuous load must be taken at 125% when sizing both the conductor and its overcurrent device
Inputs used
- Circuit Load
- 20
Intermediate steps
- Ampacity of recommended gauge
- 20 A
Confidence note: This is ampacity-only sizing — long runs may also need a thicker gauge to control voltage drop (see the Wire Gauge Voltage Drop Calculator).
What this calculation does not cover
- Copper on the 60 °C column, and nothing else. There is no input for conductor material or insulation rating, so aluminium — which carries less than copper at the same gauge — comes out undersized, and 75 °C or 90 °C rated cable comes out conservative even where every termination would allow the higher column.
- No derating is applied. Ambient temperature above the table's basis, several current-carrying conductors bundled in one cable or raceway, and sun-exposed rooftop runs all cut a conductor's usable ampacity below the table figure, and none of those conditions is an input here. The gauge returned is a floor for ideal conditions, not a finished answer.
- Run length and voltage are not part of this calculation. A 3 m run and a 60 m run at the same amps return the same gauge, and on a long run voltage drop, not ampacity, is usually what sets the size.
- This is not a load calculation and not a circuit design. It converts an amp figure you supply into a conductor size; it does not work out what that figure should be, does not apply the continuous-load 1.25 uplift for you, and does not size the neutral, the equipment grounding conductor or the overcurrent device. Motor, air-conditioning and welder circuits follow their own sizing rules and their nameplate ratings rather than a straight table lookup against running current.
- The table ends at 1 AWG (110 A). Anything needing 1/0 or larger — most services and main feeders — plus parallel conductor sets and the reduced-size allowance the code gives dwelling service conductors, is outside what this returns; a figure above 110 A does not get a valid answer here.
Add the equipment this sizes
This result is a specification — 12 AWG — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations2
- Standard copper conductor ampacity (NEC Table 310.16, 60°C column, typical for residential NM-B cable): 14 AWG=15A, 12 AWG=20A, 10 AWG=30A, 8 AWG=40A, 6 AWG=55A, 4 AWG=70A, 3 AWG=85A, 2 AWG=95A, 1 AWG=110A
- NEC 210.19(A)(1) and 210.20(A): a continuous load must be taken at 125% when sizing both the conductor and its overcurrent device
Which documents these citations point at
- National Electrical Code (NFPA 70) — Table 310.16, 210.19(A)(1) (United States)Electrical installations — conductor sizing and protection, load calculation, wiring methods, grounding and working clearances.
A code or standard has force only where a jurisdiction has adopted it, usually with local amendments. This site holds no adoption data for any authority, so check what is in force with the authority where you build. Any section cited above without an edition should be checked against the edition in force where you build. What it would take to know.
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