Complete Guide to World Time Zones
Understanding how the world divides time into zones
What Are Time Zones?
Time zones are regions of the Earth that have the same standard time. Instead of every location having its own local time, time zones allow clocks to be synchronized across larger areas.
The Earth is divided into 24 time zones, roughly corresponding to 15° of longitude each (360° ÷ 24 = 15°). This means each time zone represents one hour of Earth's rotation.
Understanding UTC Offset
UTC (Coordinated Universal Time) is the world's time standard. Local times are expressed as offsets from UTC:
- UTC+0 - London, Dublin, Lisbon (when not observing DST)
- UTC+1 - Paris, Berlin, Rome (when not observing DST)
- UTC-5 - New York, Miami, Toronto (when not observing DST)
- UTC+8 - Beijing, Singapore, Perth
Major World Time Zones
| Region | Standard Offset | Major Cities |
|---|---|---|
| Pacific | UTC-8 to UTC-10 | Los Angeles, Vancouver, Honolulu |
| Mountain | UTC-7 | Denver, Phoenix |
| Central | UTC-6 | Chicago, Mexico City |
| Eastern | UTC-5 | New York, Toronto, Miami |
| Atlantic | UTC-4 | Halifax, San Juan |
| Europe | UTC+0 to UTC+2 | London, Paris, Berlin |
| Middle East | UTC+3 to UTC+5 | Dubai, Mumbai, Karachi |
| Asia | UTC+5 to UTC+9 | Singapore, Tokyo, Seoul |
| China | UTC+8 | Beijing, Hong Kong |
| Japan | UTC+9 | Tokyo, Osaka |
| Australia | UTC+8 to UTC+10 | Perth, Sydney, Brisbane |
| Pacific | UTC-10 to UTC+12 | Auckland, Fiji |
Time Zone Database
Computers use the IANA Time Zone Database (also known as tzdata) to handle time zones. This database contains:
- Current UTC offset for each zone
- Historical time zone changes
- DST rules for each zone
- Time zone abbreviation mappings
Examples of IANA time zone names:
- America/New_York - Eastern Time
- America/Los_Angeles - Pacific Time
- Europe/London - GMT/BST
- Asia/Tokyo - Japan Standard Time
Daylight Saving Time
Many regions observe Daylight Saving Time (DST), which shifts clocks forward by one hour during summer months:
- USA - 2nd Sunday March → 1st Sunday November
- EU - Last Sunday March → Last Sunday October
- Australia - 1st Sunday October → 1st Sunday April
This causes time zones to effectively change twice per year in regions observing DST.
Special Time Zones
Some unique time zones exist:
- China (UTC+8) - Uses single time zone despite spanning 60° of longitude
- India (UTC+5:30) - 30-minute offset, not full hour
- Nepal (UTC+5:45) - Unusual 45-minute offset
- French Polynesia (UTC-10 to UTC-9:30) - 30-minute increments
Related Resources
Last updated: April 2026