UTM to Latitude/Longitude Converter

How to Read a UTM Coordinate

A UTM coordinate is written as 19K 582010 E 7466099 N: zone 19, band K, 582,010 metres east and 7,466,099 metres north. That is the main square of San Pedro de Atacama, the same position that reads -22.9111, -68.2003 in geographic coordinates.

The UTM system splits the Earth into 60 zones, each 6° of longitude wide, numbered eastward from the 180° meridian. Inside each zone, position is measured in metres:

• Easting: distance from the zone's central meridian, which is given the value 500,000 m so there are no negative numbers. An easting of 582,010 is 82 km east of that meridian.
• Northing: in the northern hemisphere it is the distance from the equator. In the southern hemisphere the equator is set to 10,000,000 m and the number falls toward the pole, so 7,466,099 is 2,534 km south of the equator.

The zone comes from the longitude:

$$\text{Zone} = \left\lfloor \frac{\text{longitude} + 180}{6} \right\rfloor + 1$$

For San Pedro de Atacama (longitude -68.2): (−68.2 + 180) ÷ 6 = 18.6, whole part 18, plus 1 gives zone 19.

Because easting and northing are in metres, subtracting two UTM coordinates in the same zone gives ground distances directly. That is why topographic maps carry a UTM grid, and why we prefer it for map-and-compass navigation.

Reference Coordinates in Chile (WGS84)

The summits are approximate points: good for finding the mountain on the map, not for navigating the last few metres.

Decimal Degrees and Degrees, Minutes and Seconds

Geographic coordinates are written two ways. Google Maps and most apps use decimal degrees (-22.9111). Nautical charts, reports and many older GPS units use degrees, minutes and seconds (22°54'40" S).

$$\text{Decimal} = \text{degrees} + \frac{\text{minutes}}{60} + \frac{\text{seconds}}{3600}$$

Example with the latitude of San Pedro: 22 + 54 ÷ 60 + 40 ÷ 3,600 = 22.9111. Being a southern latitude, it becomes -22.9111.

How much ground each figure covers:

Five decimals are enough for anything in the mountains. A handheld GPS is off by 3 to 5 metres under open sky, so the sixth decimal tells you nothing.

The Datum: WGS84, SIRGAS, PSAD56 and SAD69

The datum is the model of the Earth that coordinates are measured on, and two different datums give different numbers for the same point. This converter works only in WGS84, used by GPS units, sports watches, Google Maps and GPX files.

• SIRGAS-Chile, the current official datum, matches WGS84 to within centimetres. For navigation they are the same.
• PSAD56 and SAD69 appear on older IGM sheets. The same coordinate read as WGS84 lands up to several hundred metres away. This converter does not do that transformation.

Before entering a point from a paper map into your GPS, check the datum in the margin. And when you pass a coordinate to someone else, tell them the format and the datum: a UTM point without zone and hemisphere cannot be located.

Where It Helps When Planning a Trip

1. Moving a point from the map to the GPS. Read the easting and northing off the map grid, convert them and load the point as a waypoint in decimal degrees.
2. Giving a position by radio or satellite phone. Keep the key points of the route (camp, summit, vehicle) written down in the format the person receiving them uses.
3. Checking a track. If a point does not fall where it should, open the file with the GPX, KML and KMZ converter and compare the coordinates with the map.
4. Navigating by compass. With two UTM points you can work out distance and bearing, then correct the bearing with the magnetic declination. To measure on paper there is the map scale converter.

The summits in the table are on the Atacama interactive map. If you want to climb one with a guide, see the Licancabur volcano ascent.