DMS vs Decimal Degrees vs DDM: Which Coordinate Format Should You Use?

Open three different mapping tools and you might get three differently formatted coordinates for the exact same spot. That's not an error — latitude and longitude can be expressed in more than one notation, and each one is the convention in a different field.

Decimal Degrees (DD)

Decimal Degrees writes the whole coordinate as a single signed number, like 51.477850, -0.001470. Positive latitude is north, negative is south; positive longitude is east, negative is west. This is the format used internally by GPS chips, mapping APIs, spreadsheets and databases, because it's trivial to store, compare and do arithmetic on.

Degrees Minutes Seconds (DMS)

DMS splits the degree into 60 minutes, and each minute into 60 seconds, written as 51°28'40.3"N 0°0'5.3"W. It's the oldest of the three formats and the one still used on printed maps, in surveying, and in most legal land descriptions, because it maps directly onto how angles have been measured for centuries.

Degrees Decimal Minutes (DDM)

DDM is a middle ground: degrees stay whole, but minutes become a decimal instead of splitting into seconds — 51°28.671'N 0°0.088'W. This is the format you'll see on marine GPS units and in aviation flight plans, largely because it matches how those instruments have historically displayed position.

• Building software or working with a spreadsheet → Decimal Degrees
• Reading a paper map, deed or survey → DMS
• Filing a marine or flight plan → DDM

Converting by hand

To go from DD to DMS: the whole number is the degrees. Multiply the remaining decimal by 60 to get minutes; the whole number of that result is the minutes value. Multiply what's left after that by 60 again to get seconds. For 51.477850°, the decimal .47785 × 60 = 28.671 minutes, and .671 × 60 = 40.3 seconds — giving 51°28'40.3". It's mechanical but easy to make small errors in, which is the main reason most people reach for a converter instead of doing it by hand more than once.