International Date Line

Time and longitude

The Earth turns 360° in 24 hours, so every 15° of longitude is one hour of solar time and every degree is 4 minutes. A place on the 180° meridian is 12 hours from Greenwich in solar time, whether you count east or west. That is the root of the date line.

Civil time zones round these solar offsets to whole or half hours and follow borders, so clocks and the sun agree only roughly.

How to use it

1. The line is drawn in orange across the whole map as soon as the page opens.
2. Pan and zoom to follow it. On the web map's Mercator projection, parallels are straight horizontal lines and meridians straight vertical ones.
3. Under the map, read the list of countries whose land the line crosses and the notes about the line.
4. Use the other line pages linked below to compare positions, or the miles per degree calculator for the length of a degree at this latitude.

Why the international Date Line is there

Time zones run 15° apart east and west of Greenwich, so on the far side of the world the zones meet with a full day between them. The date line is where that day changes. Following the 180° meridian keeps it almost entirely at sea.

Countries decide which side they are on, which is why the line bends. Clock offsets on either side show how far apart the calendars are. In January 2026, Pacific/Kiritimati is UTC+14 and Pacific/Pago_Pago in American Samoa is UTC-11, a gap of 25 hours between places in the same ocean.

How long a meridian is

A meridian runs from pole to pole along the ellipsoid. Because the Earth is flattened, a degree of latitude is shorter near the equator than near the poles. Summing the meridional radius of curvature from 90° S to 90° N on WGS84 gives 20,003.9 km, or 12,430 miles, for one meridian.

The equator is longer, 20,037.5 km for half of it, because the equatorial radius exceeds the polar one. The miles in a degree guide has the full table.

What the map shows

The map draws the line itself. No country list is given here, because the line's position follows national choices rather than a single parallel or meridian.

• The line is a convention with no treaty behind it, so it is not a single meridian.
• Big Diomede (Russia, UTC+12) and Little Diomede (US, UTC-9 in winter) sit on either side of it, 21 clock hours apart in winter.
• This map draws 180° with simplified jogs around Chukotka, the Aleutians and Samoa. It does not trace every bend, such as the large eastward jog around Kiribati's Line Islands.

The United States and this line

The Aleutian Islands of Alaska straddle the 180° meridian, and the line bends west around them so all of Alaska keeps one date. Across the Bering Strait, Asia/Anadyr is UTC+12 in January while America/Nome is UTC-9, 21 clock hours apart across a strait. Honolulu, at -157.858°, is 22.1° east of the 180° meridian.