There are 60 longitudinal projection zones numbered 1 to 60 starting at 180°W. Each of these zones is 6 degrees wide, apart from a few exceptions around Norway and Svalbard.
There are 20 latitudinal zones spanning the latitudes 80°S to 84°N and denoted by the letters C to X, ommitting the letter O. Each of these is 8 degrees south-north, apart from zone X which is 12 degrees south-north.
Areas are referenced by quoting the longitudinal zone number, followed by the latitudinal zone letter. For example, the southern end of South America is 19F.
Within each longitudinl zone the transverse mercator projection is used to give co-ordinates (eastings and northings) in metres.
For the eastings, the origin is defined as a point 500,000 metres west of the central meridian of each longitudinal zone, giving an easting of 500,000 metres at the central meridian.
For the northings in the northern hemisphere, the origin is defined as the equator.
For the northings in the southern hemisphere, the origin is defined as a point 10,000,000 metres south of the equator.
The co-ordinates thus derived define a location within a UTM projection zone either north or south of the equator, but because the same co-ordinate system is repeated for each zone and hemisphere, it is necessary to additionally state the UTM longitudinal zone and either the hemisphere or latitudinal zone to define the location uniquely world-wide.
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For further details of the referencing of Grid Co-ordinates within the UTM zones, it is recommended that you visit:
For conversions between latitude/longitude and UTM co-ordinates, see: