How long is 13 full moons?

Thirteen full moons occur over a period of approximately 12 months. Since a lunar cycle, or the time between one full moon and the next, is about 29.5 days, 13 full moons would take around 354 days to complete. This is about 11 days shorter than a typical calendar year, which is why some years can have 13 full moons, often referred to as a "blue moon" when the second full moon occurs in a single month.