The chart is based on solid wire. Stranded wire (more flexible) has a slightly larger overall diameter for the same gauge. Most printed charts omit this, leading to DIYers buying stranded wire that won’t fit into a push-in connector.
By providing resistance per foot, the chart allows professionals to calculate voltage drop over long runs (e.g., 100+ ft from a solar panel to a charge controller). This is something cheap online calculators often get wrong.
Good charts include ampacity for 60°C, 75°C, and 90°C insulation. This is vital for matching wire to breaker terminals (most breakers are rated 60/75°C). The Cons – Where It Confuses Users 1. The Inverted Logic New users constantly ask: “Why does a smaller number mean bigger wire?” The historical reason (drawing dies) doesn’t help. The chart does nothing to explain this cognitive hurdle.
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.