Time Zone Converter

General Overview

Definition of Time Areas

Time areas are parts of the world where the same time is used. They often follow country borders or lines of longitude.

Greenwich Mean Time is based on the solar time at zero degrees longitude at Greenwich, London. It’s a time area. Meanwhile, Coordinated Universal Time is a global time standard used for regular civil time.

Some African and Western European nations use Greenwich Mean Time as their time area. However, Coordinated Universal Time is the standard today, guided by atomic clocks and Earth’s rotation. Unlike Coordinated Universal Time, daylight-saving time does not affect it. However, some nations change time areas in the summer, like Britain adopting British Summer Time.

Most time areas on land offset from Coordinated Universal Time. Coordinated Universal Time separates time into days, hours, minutes, and seconds, often using the Gregorian calendar. Usually, these time areas differ from Coordinated Universal Time by whole hours, like Coordinated Universal Time-05:00 or Coordinated Universal Time+08:00. However, some difference by half or quarter hours, like Coordinated Universal Time+06:30 or Coordinated Universal Time+12:45.

Global Time Area Layout

Time varies globally and used to vary more widely. By 1929, most countries had established hourly time areas. Nepal adopted a standard time area last in 1956, with the uncommon offset Coordinated Universal Time+5:45.

Generally, each 15° longitude change requires a 1-hour time change, but exceptions exist. For example, China and India use one time area, despite spanning more than 15° longitude. Conversely, Russia has 11 time areas, once reduced to 9. Time area standards are inconsistently applied internationally and can change.

Time Area Layout in the United States

The United States uses nine time areas. A 15° longitude change typically results in a 1-hour time difference.

The major time areas in the contiguous United States include Eastern, Central, Mountain, and Pacific.

• Eastern Time Area (ET): This area is Coordinated Universal Time-05:00 and covers 22 eastern U.S. states and parts of Canada, Mexico, Panama, and the Caribbean.
• Central Time Area (CT): Positioned at Coordinated Universal Time-06:00, this area includes parts of Canada, the United States, Mexico, Central America, some Caribbean islands, and the Eastern Pacific. Nine states are fully in this area, while eleven overlap with Mountain or Eastern Time areas.
• Mountain Time Area (MT): This area is Coordinated Universal Time-07:00 and includes portions of Canada, Mexico, and the United States. Five states are entirely within this area, with ten overlapping Pacific or Central Time areas.
• Pacific Time Area (PT): At Coordinated Universal Time–08:00, this area covers parts of Canada, the western United States, and western Mexico. Washington and California are fully within this area. It overlaps the Mountain Time Area, and Alaska Time Area in some places.

Additional time areas—Atlantic, Alaska, Hawaii-Aleutian, Samoa, and Chamorro—cover the rest of the United States, including Alaska, Hawaii, and U.S. territories.

These areas have standard time offsets from Coordinated Universal Time ranging from Coordinated Universal Time-04:00 to Coordinated Universal Time+10:00, with some observing daylight saving time.

Areas that observe daylight saving time adjust their clocks one hour closer to Coordinated Universal Time, while Atlantic, Samoa, and Chamorro areas do not observe this time change.

The Shift for Longer Days

Daylight-saving time involves increasing clock time by one hour in spring. In fall, it involves decreasing it to use more daylight in Europe and North America.

This clock adjustment connects work hours to sunrise and sunset better. However, it’s less effective near the equator. There, daylight varies little throughout the year.

High-latitude areas also find this adjustment less effective. This is because work hours and daylight are far apart in these areas.

Some places choose not to follow daylight saving time. This is because they have stable sunlight hours and want to keep a consistent clock throughout the year.