UTM zones explained

What UTM is

UTM replaces angles with meters. Each zone has its own transverse Mercator projection centered on the zone's middle meridian, and a position is written as a zone, an easting and a northing. Within one zone, distances can be measured with a ruler because the grid is square and in meters. The USGS notes that neither UTM nor latitude and longitude is more accurate; they are two ways of writing the same position.

Per the USGS, zones are numbered 1 to 60 starting at 180° and increasing eastward. Zone 19 is the easternmost zone in the contiguous states and includes Maine.

Easting and northing

The easting is the distance in meters east of a false origin set 500,000 m west of the zone's central meridian, so every easting in the zone is positive. The northing is the distance north of the equator in the Northern Hemisphere. The converter on this site applies the standard scale factor of 0.9996 on the central meridian and the WGS84 ellipsoid. Denver's capitol, for example, is zone 13, easting 501,285 m, northing 4,398,790 m.

How many counties sit in each zone

Counting county internal points, zone 16 holds the most, 673 of 3,144. 40 of the 51 states and DC have county points in more than one zone, and Alaska spans the most, with 8. Counties that straddle a zone edge are counted once, by their internal point.

UTM coordinates of every state capital

Working across a zone edge

Coordinates from two zones cannot be compared directly, because each zone has its own origin. A project that spans an edge either picks one zone and accepts growing distortion outside it, or switches to latitude and longitude. Each state page lists the zones its counties fall in, for example Alaska.

How to read a UTM coordinate

A full UTM position has three parts: the zone with its hemisphere letter, the easting and the northing. Denver's capitol is written 13N 501,285 4,398,790. Read it as: zone 13, northern hemisphere, 501.3 km east of the false origin and 4,398.8 km north of the equator.

Because the grid is in meters, a point 1 km east is simply 1,000 more in easting. That makes UTM convenient for field work, where you can pace or measure distances and add them to a coordinate without trigonometry.

Converting to latitude and longitude

The conversion runs the transverse Mercator equations backward from the zone's central meridian. It needs the zone number; an easting and northing without a zone could be anywhere around the world at that latitude. The UTM converter below does both directions. Most errors come from a wrong zone or a swapped easting and northing, so check that the easting has six digits and the northing, in the US, has seven.

Distortion inside a zone

Each zone is narrow so that its projection stays close to true scale. The central meridian is shrunk by the 0.9996 scale factor, and scale grows toward the zone edges, passing 1.0 on two lines about 180 km either side of center. Within one zone the error stays small enough for most mapping and field work. Across several zones, as in Alaska with 8, it does not, and a single-zone grid for the whole state would stretch distances near its far edges.