What Is Longitude?

Longitude describes how far east or west a place is from the prime meridian. Paired with latitude, it identifies a position on Earth. Our location finder can provide both coordinates for an address or your current location.

How Longitude Works

The prime meridian is 0 degrees longitude and passes through Greenwich, England. Longitude extends east and west to 180 degrees, where the two directions meet near the international date line. Lines of longitude run from pole to pole and are called meridians.

• A positive longitude is east of the prime meridian, often written with an E.
• A negative longitude is west of the prime meridian, often written with a W.
• Every valid longitude falls between -180 and 180 degrees.

How to Read a Longitude Coordinate

Longitude can be written in decimal degrees or in degrees, minutes, and seconds. In a standard latitude-longitude pair, longitude is the second number. A pair such as 39.9526, -75.1652 therefore gives latitude first and longitude second.

Longitude and Time Zones

Earth rotates 360 degrees in about 24 hours, so 15 degrees of longitude corresponds roughly to one hour of solar time. Actual time-zone borders follow political and practical boundaries, however, so longitude alone does not determine a location's official time zone. Use our time-zone finder when you need the local time zone for an address.

Why Longitude Is Useful

Longitude is essential for GPS, navigation, mapping, surveying, travel, and emergency response. Because meridians meet at the poles, the ground distance represented by one degree of longitude becomes smaller as you move away from the equator.

To understand the first number in a coordinate pair, read our guide to how latitude coordinates work.

Additional Resource

The National Ocean Service longitude guide covers the history and science behind measuring longitude.