String sizing determines the optimal number of solar modules to connect in series based on inverter specifications and temperature conditions. Per NEC 690.7, maximum system voltage must be calculated at the coldest expected temperature, as module voltage increases in cold weather and decreases in hot weather. This calculator ensures strings operate within the inverter MPPT window at hot temperatures for maximum energy harvest, while staying below maximum input voltage at cold temperatures to prevent equipment damage. Proper string sizing prevents overvoltage damage, optimizes efficiency, ensures code compliance, and maximizes performance across all conditions.