Coordinate Converter

One position, four ways of writing it

A GPS receiver, a paper map, a search warrant and a geocache listing can all describe the same spot in different notation. Decimal degrees (DD) write latitude and longitude as signed numbers: the Empire State Building is at 40.748440, −73.985664, where the minus sign means west of Greenwich. Degrees, minutes and seconds (DMS) divide each degree into 60 minutes and each minute into 60 seconds, giving 40°44′54.4″ N, 73°59′08.4″ W. Degrees and decimal minutes (DDM), the format most handheld GPS units and geocaching sites use, give 40° 44.906′ N, 73° 59.140′ W. Conversion is simple arithmetic: decimal degrees = degrees + minutes ÷ 60 + seconds ÷ 3,600, with south and west negative.

What the decimals mean on the ground

One degree of latitude is about 111 km everywhere, so a minute is about 1.85 km, the length of a nautical mile, and a second is about 31 m. The sixth decimal place of a degree is about 11 cm, which is already finer than a phone GPS can resolve; writing eight decimals implies millimetre precision nobody has. Longitude degrees shrink towards the poles in proportion to the cosine of the latitude: at New York’s 40.7° N a second of longitude is about 23 m, and at 60° N it is about 15 m. A common mistake is to drop the minus sign or the W when copying a longitude, which moves a point in Manhattan to the mountains near the Kyrgyz–Chinese border.

UTM grid references

The Universal Transverse Mercator grid replaces angles with metres. The world between 80° S and 84° N is divided into 60 zones, each 6° of longitude wide, and each zone is projected onto its own flat grid. Eastings are measured from a false origin 500,000 m west of the zone’s central meridian, so they are always positive; northings are measured from the equator in the northern hemisphere and from 10,000,000 m south of it in the southern hemisphere. The Empire State Building is 18T 585631 m E, 4511327 m N: zone 18, latitude band T, about 85.6 km east of the 75° W central meridian. Sydney Opera House, at −33.8568, 151.2153, is 56H 334901 E, 6252289 N. Because UTM is in metres, two grid references 1,000 m apart in easting are exactly 1 km apart on the map, which is why search-and-rescue and military maps print a UTM grid.

Datums and exceptions

Every conversion here assumes WGS84, the datum GPS uses. Older paper maps may be printed on NAD27 in North America or OSGB36 in Britain, and the same latitude and longitude can sit tens to hundreds of metres apart on different datums, so check the map margin. UTM has two zone exceptions: zone 32 is widened over south-western Norway, and zones 31 to 37 are rearranged around Svalbard. The converter applies both. Near a zone boundary, a point can have valid grid references in two zones; maps that straddle a boundary usually print both grids.

How to use it

1. Choose whether you are entering latitude and longitude or a UTM grid reference.
2. Type the latitude and longitude in any common form: 40.7484, 40 44 54.4 N or 40°44.906′N.
3. For UTM, enter the zone, hemisphere, easting and northing in metres.
4. Read the position in all four formats and copy the one your map or device expects.