Live departure crowding at Seattle-Tacoma Airport. Each bar is one departure, drawn from the moment passengers turn up until boarding closes. Where bars stack, the terminal is full.
The load curve is relative, not a headcount: every flight is weighted equally, so 100% is simply the busiest minute of the day shown. A day of small propliners and a day of full charters look the same — what the curve tells you is when the building fills up, not by how much. Times are shown in the airport's own timezone. Data refreshes every 5 minutes.
Airport departure boards tell you when flights leave, but not how crowded the building will be. This page draws every departing flight as a bar spanning the time its passengers are inside the terminal — from arrival (default 3 hours before departure) until boarding closes — and sums the overlaps into a per-minute relative load curve. The peak of that curve is the moment to avoid, or to aim for if you like queues short.