On any given day, more than 87,000 flights are in the skies in the United States. Only one-third are commercial carriers, like American, United or Southwest. On an average day, air traffic controllers handle 28,537 commercial flights (major and regional airlines), 27,178 general aviation flights (private planes), 24,548 air taxi flights (planes for hire), 5,260 military flights and 2,148 air cargo flights (Federal Express, UPS, etc.). At any given moment, roughly 5,000 planes are in the skies above the United States. In one year, controllers handle an average of 64 million takeoffs and landings.
For every one flight you see listed on an airport monitor, two you don't see show up on air traffic controllers' screens. It would take approximately 7,300 airport terminal monitors to show all the flights controllers handle in a single day and approximately 460 monitors to show the number of flights being handled at any one time.
http://www.natca.org/mediacenter/bythenumbers.msp