The right conductor by NEC ampacity and voltage drop — with continuous load, derating, and terminal limits handled. Get the wire, the breaker, and the ground.
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Sizing a conductor is really two questions. Ampacity asks: what's the smallest wire that carries this current without cooking its insulation — after you knock it down for a hot attic or a packed raceway, and cap it at what the breaker lugs are rated for. Voltage drop asks: what's the smallest wire that still delivers healthy voltage at the far end of a long run. On short runs ampacity wins; on long homeruns, EV chargers, and outbuildings, voltage drop usually forces a bigger wire. The honest answer is the larger of the two — which is exactly what this returns, along with the breaker and the equipment ground that go with it.
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For reference and estimating only. Based on NEC (NFPA 70) 2023 — Table 310.16, 110.14(C), 240.4, 240.6, 310.15, 250.122 — and the standard K-method for voltage drop. Not a substitute for the National Electrical Code, a licensed electrician's judgment, or your authority having jurisdiction. Confirm terminal ratings, load type, and conditions of use, and verify every result against your locally adopted code before installing.