GPS Coordinates Converter

Three ways to write the same point

• Decimal degrees. 40.179333, 44.508333. What every mapping API, database and spreadsheet wants. Latitude first, negative for south and west.
• Degrees, minutes, seconds. 40°10'45.6"N. What paper maps, land registries and old survey documents use. A minute is a sixtieth of a degree; a second is a sixtieth of that.
• Degrees and decimal minutes. 40°10.760'N. What marine and aviation use, and what a chart plotter or a VFR flight plan expects. It exists because one minute of latitude is one nautical mile, so tenths of a minute are a unit a navigator can do arithmetic in.

Decimal places are a claim about accuracy

One degree of latitude is about 111 kilometres everywhere. Each decimal place divides that by ten: three places is roughly 110 metres, five places is about a metre, seven places is a centimetre. A phone GPS is good to somewhere between three and ten metres in the open and much worse in a city, so a coordinate written to seven decimal places is claiming a precision the device never had. Longitude is different — a degree of longitude is 111 km at the equator and shrinks with the cosine of the latitude, down to nothing at the poles. At 60° north it is half. The table above works both out for the point you entered.

The mistakes that actually happen

The big one is the swap: longitude written first, which puts a point in Yerevan into the Indian Ocean instead. This tool catches it when the numbers make it obvious or when you have labelled the hemispheres, but it cannot catch a swap between two values that are both valid as either. The second is a dropped minus sign, which reflects a point across the equator or the prime meridian — most of the time into open water, which at least makes it visible. The third is mixing formats in one string: 40.10 45.6 is not a coordinate in any of the three notations, and something will read it as one anyway.

A word on datums, which is shorter than you fear

A coordinate is a position on a mathematical model of the earth, and there is more than one model. Everything on this page is WGS84 — the datum GPS satellites broadcast in, and the one your phone, your car and every consumer receiver report. If you are reading coordinates off a national survey map you may be in a local datum instead: OSGB36 in Britain, NAD83 in North America, Pulkovo 1942 across the former Soviet Union. The shift between datums can be hundreds of metres, which is more than every decimal place you were arguing about. Converting between datums is a different job from converting between notations, and this tool does not do it. If your source does not say which datum it is in and it came from a GPS device, it is WGS84.