Cerro Wire, PowerStream Technology and Armstrong's Supply Company's websites are some online resources that provide wire size vs. amps charts. Cerro Wire provides a chart of different wire gauge sizes and amp ratings for both copper and aluminum wire at different ambient temperatures.
The Armstrong's Supply Company and PowerStream Technology also provide similar charts. The chart provided by Armstrong's Supply Company shows gauge sizes and their appropriate ampacities at different ambient temperatures.
PowerStream Technology also gives metric wire gauges. PowerStream Technology also explains that an increase in gauge size wires corresponds to a decrease in wire diameters. Similarly, the amp rating refers to amperage, which is the measure of the current that goes through an electrical circuit.