The chart’s most valuable column is ampacity (current-carrying capacity). It prevents fires: a 14 AWG wire is rated for 15A, 12 AWG for 20A, 10 AWG for 30A, etc. Ignoring this is the #1 cause of residential electrical fires.
4/5 – Indispensable for pros, dangerous for amateurs without a disclaimer. awg wire size chart
you understand NEC derating. Avoid it if you just want to know “what wire for a 20A breaker?” – in that case, memorize: 14 AWG = 15A, 12 AWG = 20A, 10 AWG = 30A and ignore the chart’s complexity. 12 AWG for 20A