UTM converter

Type a latitude and longitude in any common form: 40.748440, -73.985664, or N 40° 44.906 W 73° 59.140, or with degrees, minutes and seconds. The result gives the UTM position (zone and band, easting, northing) and the MGRS reference, and the rows add the scale factor and grid convergence there. Links open the point in a map app; nothing is sent until you follow one.

Type a UTM position instead, such as 18T 585631 4511326 or 18 north 585631 4511326, or an MGRS reference, and you get latitude and longitude back.

UTM, the Universal Transverse Mercator system, cuts the world into 60 zones, each 6° of longitude wide, numbered eastward from 180°. Each zone gets its own flat map, a transverse Mercator projection centred on the zone's middle meridian, so within a zone a position is just metres east and metres north.

Eastings count from 500,000 m at the central meridian, so they're never negative. Northings count from the equator, which is 0 in the northern hemisphere and 10,000,000 m in the southern, again to keep them positive. The scale is set 0.9996 on the central meridian, which keeps distortion within about 1 part in 1,000 across the zone.

MGRS, the Military Grid Reference System NATO uses, writes the same UTM position in three parts. 18T is the grid zone: zone 18 and latitude band T, one of the 8° bands lettered C to X from 80° S (I and O are skipped, and X is 12° tall). WL names the 100 km square inside it, a column letter and a row letter. The digits are the metres east and north inside that square, as two equal halves.

Fewer digits name a bigger square: 10 digits pin a 1 m square, 8 a 10 m square, 6 a 100 m square. The digits are cut short, never rounded, so a shorter reference always names the square the point is in. Read back, a reference gives the centre of its square.

Wikipedia's article on MGRS uses Honolulu: 21°24′35.43″ N, 157°54′57.89″ W. That's zone 4, since 157.9° W is in the 4th 6° strip east of 180°, and band Q, which covers 16° N to 24° N. Projected onto zone 4 it's 612,344 m east and 2,367,894 m north. The 100 km square is FJ, so to 10 m the reference is 4Q FJ 1234 6789, the article's own example. Typed back in, that reference gives the centre of the 10 m square, the same point.

Two places break the 6° rule. Off south-west Norway, zone 32 is widened 3° to the west between 56° N and 64° N, and zone 31 shrinks to open sea. Around Svalbard, from 72° N to 84° N, zones 32, 34 and 36 aren't used, and 31, 33, 35 and 37 are widened to cover them. The converter applies both.

UTM stops at 84° N and 80° S. Closer to the poles, maps use the Universal Polar Stereographic grid, which this page doesn't convert.