Stranger Things Season 1 consists of 8 episodes. The first season was released as eight episodes in total, each varying in length from approximately 42 to 55 minutes. This season was originally conceived as an eight-hour sci-fi horror story, which is why it has 8 episodes.

If you meant "volume 1" in a different season context (such as season 5 split into volumes), please specify, but for the original Season 1 of Stranger Things, there are 8 episodes.