Decimal Degrees vs Degrees Minutes Seconds

Decimal degrees (DD) and degrees, minutes and seconds (DMS) are two ways to write exactly the same latitude and longitude. Decimal degrees express the angle as one number with a decimal fraction, such as 37.7749. DMS splits the angle into whole degrees, minutes and seconds, such as 37 degrees 46 minutes 29.6 seconds. Neither is more correct; they suit different situations.

How each format looks

Decimal degrees use a single number per axis, with the sign showing direction:

37.7749, -122.4194

Degrees, minutes and seconds use three parts and a hemisphere letter:

37° 46' 29.6" N, 122° 25' 9.8" W

There is also a middle format, degrees and decimal minutes, such as 37° 46.494' N, which you sometimes see on marine and aviation equipment.

The relationship between the units

One degree is divided into 60 minutes, and one minute into 60 seconds, the same way hours are divided in time. That means one minute is 1/60 of a degree and one second is 1/3600 of a degree. The same position can therefore always be converted from one format to the other; see how to convert DMS to decimal degrees for the formula.

Strengths of decimal degrees

• One number per axis makes storage, sorting and calculation straightforward.
• It is the format used by almost all web maps, databases and APIs.
• It is easy to copy and paste, with no special symbols to mistype.

The downside is readability: a long string of digits is harder for a person to picture than a familiar unit.

Strengths of DMS

• It follows the traditional way of reading charts, surveying and navigation.
• Seconds are a natural unit for people thinking in small distances, because one second of latitude is a little over 30 metres.
• Printed maps, legal land descriptions and many older documents use it.

The downsides are the extra symbols, the hemisphere letters that must not be forgotten, and the awkwardness of calculating with base-60 numbers.

Which one to use

Use decimal degrees when you are writing software, storing data or calling an API. Use DMS when you are reading a chart or a document that was written in it, or when your audience expects it. Whichever you pick, state the format clearly and keep the order consistent, as explained in latitude first or longitude first.

For a refresher on what the numbers actually represent, see what latitude and longitude are.