Coordinate converter

Specific conversions

Need a single direction rather than the all-in-one tool above? Jump straight to it: convert DMS to decimal degrees for coordinates off a map margin or field notes, turn decimal degrees into DMS for a deed or a printed chart, write decimal degrees as degrees decimal minutes for a marine or aviation GPS, project latitude and longitude into UTM metres for surveying, reproject to Web Mercator (EPSG:3857) for web-map tiles, or go the other way, from projected metres back to decimal degrees.

How to use it

1. Type or paste your latitude and longitude, in decimal degrees, DMS (48°51'30"N) or DDM (48°51.5'N). The format is detected automatically.
2. Every other format updates as you type. Click Copy on any row.
3. Web Mercator and UTM are computed with the industry-standard proj4 library, loaded once and cached.

The formats, briefly

Decimal degrees (DD), a single signed number per axis (48.8584, 2.2945). Compact and what most software and GeoJSON expect.

Degrees minutes seconds (DMS), 48°51'30"N. Traditional on maps and in surveying. DD = degrees + minutes/60 + seconds/3600 (negative for South/West).

Degrees decimal minutes (DDM), 48°51.5'N. Common on marine GPS and aviation.

Web Mercator & UTM, projected systems in metres, used by web maps (3857) and surveying/military (UTM). Useful when a tool wants X/Y in metres rather than degrees.

Which coordinate format should I use?

The right notation depends entirely on what will read it next, not on the coordinate itself. Match the format to the destination:

• Loading points into a GIS, GeoJSON or a web map → decimal degrees (WGS84). It is what almost every digital tool expects.
• Reading a paper map, a property deed or a survey report → degrees minutes seconds, the notation printed on them.
• Typing a waypoint from a boat or aircraft GPS → degrees decimal minutes, the marine and aviation default.
• Feeding a web-map tile pipeline or a tool that wants EPSG:3857 → Web Mercator, in metres.
• Surveying or engineering that works in metres → UTM, the local metre grid.

If someone hands you a coordinate with no context, the notation usually gives away where it came from: a plain pair of decimals is digital, a value with ° ' " symbols is off a map or deed, minutes with a decimal and an N/S/E/W letter is marine or aviation, and a big six- or seven-figure number in metres is projected UTM or Web Mercator. Paste it into the converter above and every other form appears at once.

The four notations compared

Decimal degrees, DMS, DDM and UTM all describe the same point on Earth; they just write it differently. Here is one location, the Eiffel Tower in Paris, in each notation (plus Web Mercator), so you can see how they line up and sanity-check your own conversions.

How to convert between them

DMS to decimal degrees: DD = degrees + minutes ÷ 60 + seconds ÷ 3600, made negative for south or west. Decimal degrees to DMS: the whole number is the degrees, multiply the remainder by 60 for the minutes, and that remainder by 60 again for the seconds. Decimal degrees to DDM: keep the whole degrees and multiply the fraction by 60 to get decimal minutes, with no seconds step. Latitude and longitude to UTM: the zone comes from the longitude (zone = floor((longitude + 180) ÷ 6) + 1) and the point is reprojected with proj4. The converter above does all of these at once; this is simply what it is doing under the hood.

Where each notation comes from

DMS is the oldest, inherited from splitting a circle into 360 degrees, each into 60 minutes and 60 seconds, the same sexagesimal system as a clock face. DDM is the navigator's simplification: minutes are easy to add and subtract at sea, and dropping seconds removes one source of error. Decimal degrees arrived with computers, because one number per axis is trivial to store, sort and calculate with. UTM and Web Mercator are projections: they trade the globe's angles for a flat grid measured in metres, which is exactly what surveying and web tiles need.

How precise do you need to be?

Precision comes down to how many decimal places you keep. Each extra decimal place of latitude is worth roughly a factor of ten on the ground:

One second of arc is already about 31 m, so converting DMS to only two or three decimal places throws away precision the original coordinate had. Five or six decimals is the safe default for mapping and survey work. For DDM, three decimal minutes is about 1.8 m, which is why marine GPS units display that many.

Why coordinates end up in the wrong place

Two mistakes cause almost every misplaced point. The first is swapping latitude and longitude: people say "lat, long", but many file formats store longitude first (X before Y), so a careless copy puts Paris in the Indian Ocean. Latitude runs -90 to 90 and longitude -180 to 180, so any value above 90 must be a longitude, a quick sanity check. The second is reading projected metres as degrees: a value like 448266 is UTM or Web Mercator metres, not degrees, and pasting it into a degree field sends the point nowhere real. If your data landed somewhere wrong, our guide on GIS data in the wrong place walks through the fixes.

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