TORONTO — It’s amazing to think how far we’ve come from the Wright brothers’ historic first flight in North Carolina over 100 years ago. Since then, aviation has flown leaps and bounds, with commercial aircraft expected to carry nearly four billion passengers this year, says IATA.

With this many passengers, we’re going to need a lot of planes. But exactly how many planes already exist in the world today?

The answer is tricky to pinpoint. Aviation analysts Ascend found that the total number of aircraft currently in service – including passenger and cargo – is approximately 23,600, reports The Telegraph. But airliners.net, an aviation enthusiast website, says that there are about 39,000 planes in the world – including all commercial and military planes – and that over the course of history, there have been 150,000.

Boeing, one of the world’s biggest aircraft manufacturers, says that 39,620 new planes will be needed over the next 20 years. This estimate puts the number of aircraft in the world at 63,220 by 2037 (not including older planes no longer in service at that time).

These numbers would indicate that the skies are becoming an increasingly crowded space. According to FlightRadar24, who tracks aircraft around the world, there are over 16,000 planes in the air at any given time on peak traffic days.

And who has the most planes nowadays? Taking figures from June 2016, the runaway leader of the pack is American Airlines with a fleet size of 1,789. In fact, the top five is made up entirely of U.S. carriers, with Ryanair clocking in at 10th place with just 363 planes.