The simplest way to figure out how full the flight will be is to pick up the phone and call the airline. Explain that you're concerned about being on a crowded flight and ask the agent to give you an estimate as to how full the flight currently is.

In 2026, you can gauge the typical "fullness" of a flight by checking a few key data points before you book. First, look at the Seat Map on the airline’s app or website; if most of the "standard" seats are occupied weeks in advance, it's a strong indicator of a high load factor. Second, check the Fare Availability; if the "Basic Economy" or lowest-priced "Saver" tickets are sold out, the airline has already filled its budget-tier quota and the plane is likely quite full. Third, you can use third-party tools like ExpertFlyer or AwardFares, which show the specific number of seats available in each fare bucket (e.g., "J9" means at least 9 Business seats remain). Another trick is to perform a search for 9 passengers on the flight; if the airline says "only 3 seats left at this price," you know the cabin is nearing capacity. Finally, consider the timing: flights on Sunday evenings, Monday mornings, or during major holiday windows are almost guaranteed to be 100% full, regardless of what the seat map looks like a month out.