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How to convert GPS coordinates: DD, DMS, and DDM explained

· 5 min read

GPS coordinates come in three common formats, and switching between them is one of those tasks that sounds simple until you're staring at a pair of numbers that don't match what your device expects. Whether you're copying coordinates from Google Maps, entering a waypoint into a marine chartplotter, or decoding a hiking trail description, you'll run into all three notations sooner or later. This guide explains what each format means, shows you how to convert by hand, and points you to a free tool that does the math instantly.

The three GPS coordinate formats

Every GPS coordinate is a pair of angles — latitude (north/south) and longitude (east/west). The angle itself doesn't change; only the notation does.

  • Decimal degrees (DD) — a single number per axis, with fractions as a decimal. The default for web maps and most APIs. Example: 40.7128, -74.0060
  • Degrees, minutes, seconds (DMS) — the traditional surveying and mapping format. One degree splits into 60 minutes; one minute into 60 seconds. Example: 40° 42' 46.1" N, 74° 0' 21.6" W
  • Degrees, decimal minutes (DDM) — a hybrid used heavily in marine and aviation GPS. Degrees stay whole; the fraction is expressed as decimal minutes rather than minutes-and-seconds. Example: 40° 42.768' N, 74° 0.360' W

If you're unsure which format a coordinate is in, check whether the number after the degree symbol has a decimal point (DDM) or is followed by a second symbol with its own decimal (DMS). Pure decimal numbers with no degree symbol are DD.

A worked example: converting DD to DMS and DDM

Let's convert the latitude 40.7128 step by step.

DD to DMS

  • The whole number is the degrees: 40°
  • Take the decimal part (0.7128) and multiply by 60: 0.7128 × 60 = 42.768. The whole number is the minutes: 42'
  • Take the remaining decimal (0.768) and multiply by 60: 0.768 × 60 = 46.08. That gives the seconds: 46.08"
  • Result: 40° 42' 46.08" N

DD to DDM

  • Degrees stay the same: 40°
  • Multiply the decimal part by 60 as above: 0.7128 × 60 = 42.768. That decimal number is the decimal minutes — you stop here.
  • Result: 40° 42.768' N

DDM is essentially DMS with the seconds folded back into a decimal minute — one less field to enter on a chartplotter.

Going back: DMS and DDM to decimal degrees

  • DMS to DD: DD = Degrees + (Minutes / 60) + (Seconds / 3600). Example: 40 + (42 / 60) + (46.08 / 3600) = 40.7128
  • DDM to DD: DD = Degrees + (Decimal Minutes / 60). Example: 40 + (42.768 / 60) = 40.7128

Don't forget: west longitudes and south latitudes are negative in DD. 74° 0' 21.6" W becomes -74.0060.

When does each format come up?

  • DD — Google Maps, Apple Maps, web APIs, most smartphone GPS apps, and share links.
  • DMS — printed topo maps, land surveys, older handheld GPS units, trail guides. See our DD vs DMS deep-dive.
  • DDM — marine chartplotters, aviation GPS, and NMEA sentences from GPS hardware.

Mixing formats is the most common source of coordinate errors. A latitude entered as 40.7128 when a device expects DDM gets misread as 40° 71.28' — impossible, since minutes only go to 59 — and plots you somewhere wrong.

Other coordinate systems worth knowing

DD, DMS, and DDM all describe the same geographic coordinates — three ways of writing the same angle. Systems like Plus Codes and what3words encode locations as short strings instead. Our guide to Plus Codes and what3words explains how they map back to lat/lon.

Skip the arithmetic — convert instantly

Manual conversion is useful once, so you understand the numbers. After that, there's no reason to do it by hand. The coordinate converter accepts DD, DMS, or DDM — paste whatever you have and it outputs all three formats. No account, no install; the conversion runs entirely in your browser. To see where those coordinates land, open the map, drop a pin, and read off your position in whichever format you need.