WIRE GAUGE (AWG)
WIRE GAUGE (AWG)
AWG = f(amps, NEC 310.16 75°C)
A
V
ft
RESULT
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NEC 310.16 75°C ampacity + 3% voltage-drop bump. Continuous loads (≥3 hr) require 125% derate — apply manually before entering amps. Estimate only — verify with a licensed electrician and local code/inspector before purchase or installation. Not a substitute for engineered drawings.
About this calculator
This wire gauge calculator returns the minimum AWG (American Wire Gauge) for a copper or aluminum conductor based on circuit amperage and run length. Sizing comes from NEC Table 310.16 at 75°C terminations (the standard for residential and commercial breakers, lugs, and panelboards). The calculator also runs a 3% voltage-drop check on the chosen size and bumps up if a long run pushes drop past code-recommended limits, since NEC 210.19(A) Informational Note 4 caps branch circuits at 3%. ESTIMATE ONLY — final wire size and install must be verified by a licensed electrician and the local AHJ before any work goes in.
Common questions
What AWG is needed for 20 amps?
12 AWG copper handles 20 A at 75°C terminations per NEC 310.16. 14 AWG is rated 15 A and pairs with a 15 A breaker only. Aluminum runs one size larger — 10 AWG aluminum is the minimum for a 20 A circuit.
When does run length force me to upsize?
Voltage drop bumps wire size when the round-trip drop exceeds 3% (NEC 210.19(A) Informational Note 4). On 12 AWG copper at 20 A and 120 V, that hits at roughly 60 ft one-way; on 240 V circuits the limit roughly doubles. Detached buildings, well pumps, and EV chargers are the usual offenders.
Do I need to derate for continuous loads?
Yes. NEC 210.19(A)(1) and 215.2 require conductor and breaker to be sized at 125% of continuous load (anything operating 3 hours or longer — EV chargers, electric heat, sign lighting). Multiply the actual load by 1.25 before entering it in the calculator.