| science | Reddit Science | 33,780,992 |
| space | /r/space: news, articles and discussion | 27,744,175 |
| Futurology | Future(s) Studies | 21,539,760 |
| biology | Biology | 5,363,743 |
| psychology | Psychology | 4,714,181 |
| math | math | 3,857,097 |
| chemistry | Reddit Chemistry - Read the sidebar | 3,769,202 |
| spacex | r/SpaceX, the premier SpaceX discussion community | 3,671,191 |
| UFOs | The UFO reddit | 3,345,634 |
| Astronomy | Astronomy | 2,994,581 |
| MachineLearning | Machine Learning | 2,957,255 |
| AskPhysics | Ask Physics | 1,440,022 |
| aliens | Aliens | 1,033,555 |
| HighStrangeness | High Strangeness | 972,308 |
| ciencia | Ciencia - Comunidad para noticias y contenido de carácter científico | 670,984 |
