The exact size of the Dying Light download depends on the platform you are playing on.
For PC, the download size is approximately 18 GB. For Xbox One, the download size is 20 GB. Finally, for PlayStation 4 the download size is 23 GB.
In addition, there may be additional patch updates or content downloads that require more space. This includes any downloadable content or updates that are released after the game is released. The size of these updates can range from a few hundred megabytes to a few gigabytes.
Finally, it is important to note that the download size of the game can also vary depending on the region you are downloading from. For example, the download size in the US may be different than the download size in Europe.
Overall, the Dying Light download size is approximately 18-23 GB, depending on the platform you are playing on.