If you're looking for summer vibes, the best time to travel to Brussels is in July, August and June, when the average temperature reaches 21.94 °C, while July, May and June are the 3 sunniest months of the year, with an average of 103.5 hours.
If you prefer colder temperatures, however, make sure you visit Brussels during the months of January, February and March to experience an average of 1.12 °C.
For those who don't care too much about temperatures, but want to avoid getting wet in the rain, it's important to avoid travelling during January, February and March, when the average precipitation in Brussels is 3.75 mm, while the months of January, February and March are drier, with an average of 0 mm.