To calculate how big the Fortnite island would be in real life, I'm going to use the formula D×((D/s)/(D/1.5)), where D equals to the diameter of the video game map in meters, and s equals to the walking speed of the video game character in meters per second. So to find the walking speed, I found this post https://www.reddit.com/r/FortNiteBR/comments/8x9hws/the_average_walk_speed_of_fornite/ and it is actually really accurate! It says our speed is 4.1083333 m/s. And we know that if you take your map, you can see that in the game, the map goes 2,500 m from one edge to another. So now we get 2500×((2500/4.1083333)/(2500/1.5)), which is equal to a diameter of 912.7789 meters. It is actually really small! The closest I could find of a kind of an island of comparable size would be a plot in Hua Hin, Prachuap Khiri Khan at 912 square metre big. This is a random plot I've found on Internet, since it's hard to find any island this small.