World Time Zones Explained: A Complete Guide
Understand how the 24 time zones work, why some countries use half-hour offsets, and how UTC coordinates global time.
World Time Zones Explained
The Earth is divided into 24 primary time zones, each roughly 15 degrees of longitude wide. In practice, political boundaries and regional decisions create many more variations.
How time zones work
The system is based on Coordinated Universal Time (UTC). Each zone is defined by a positive or negative offset from UTC:
Why 24 zones?
The Earth rotates 360 degrees in 24 hours. Dividing 360 by 24 gives 15 degrees per hour. Sir Sandford Fleming proposed this system in 1879, and the International Meridian Conference adopted it in 1884.
Countries with unusual offsets
Not all countries use whole-hour offsets:
Countries with multiple time zones
The International Date Line
The International Date Line (IDL) runs roughly along the 180° meridian in the Pacific Ocean. Crossing it westward advances the date by one day; crossing eastward moves it back by one day.
DST and time zones
About 70 countries observe daylight saving time, temporarily shifting their UTC offset by one hour. This means the number of active time zones changes throughout the year.
Explore all time zones on our [World Map](/world-map).