The Earth has 24 major time zones. This standard model follows the planet’s 24-hour rotation: dividing 360 degrees of longitude by 24 produces zones roughly 15 degrees wide, with about one hour between neighboring zones.
The system grew from the need for consistent railway and telegraph timekeeping during the 19th century. At the 1884 International Meridian Conference, delegates selected Greenwich, England, as the reference for the prime meridian, which became the basis for calculating time offsets around the world.
In practice, time-zone boundaries rarely follow neat 15-degree strips. Countries adjust them for political borders, trade, population centers, and local policy. Some places also use half-hour or 45-minute offsets, and daylight saving time changes clocks seasonally. Therefore, 24 is the canonical answer for major or idealized zones, while the number of actual civil time zones in use is higher.