MGRS Converter

In short MGRS is UTM with the leading digits replaced by letters, which makes a position short enough to read over a radio. A reference like 30UXC 99316 10163 is the UTM zone 30, the latitude band U, the 100 km square XC within that zone, and then the easting and northing inside that square. The most important property is that an MGRS reference is a SQUARE, not a point, and its length tells you which square: two digits per axis is 10 km, four is 1 km, six is 100 m, eight is 10 m and ten is 1 m. Dropping digits does not round the position, it widens the square, and the reference always names its south-west corner rather than its centre. Neither I nor O appears anywhere in the lettering, because beside 1 and 0 they are unreadable handwritten or spoken — the geohash alphabet drops the same two letters for the same reason. Two cautions. The 100 km square letters repeat in every zone, so a square identifier without the zone and band in front of it names dozens of places worldwide. And the 100 km lettering scheme depends on the datum: a reference taken from a mid-century map on ED50 or NAD27 will not agree with a WGS84 one, sometimes by hundreds of metres.