Coordinate Systems
UTM Coordinate System Explained
Summary
UTM divides the world between 80°S and 84°N into 60 zones, each 6° of longitude wide and projected with a Transverse Mercator projection. Coordinates are eastings and northings in metres, with a false easting of 500 000 m, a false northing of 0 m in the northern hemisphere and 10 000 000 m in the southern, and a central-meridian scale factor of 0.9996. Riyadh (24.7136° N, 46.6753° E) is in zone 38N at E 669,459.6 m, N 2,734,271.7 m.
Definition
UTM: a global system of 60 Transverse Mercator zones, 6° wide, with scale factor 0.9996 on each central meridian, false easting 500 000 m and false northing 0 m (north) or 10 000 000 m (south).
- 60 zones × 6°
- k₀ = 0.9996
- False easting 500 000 m
- South: false northing 10 000 000 m
- Valid 80°S – 84°N
- WGS 84 north: EPSG:326zz
How UTM zones are numbered
Zone 1 covers 180°W to 174°W and numbers increase eastward. The zone and its central meridian are:
Exceptions: zone 32 is widened over south-west Norway, and zones 31–37 are modified over Svalbard. Polar regions use the Universal Polar Stereographic (UPS) system. See UTM zones for the Middle East zone table.
Projection parameters
| Parameter | Value |
|---|---|
| Projection | Transverse Mercator |
| Latitude of origin | 0° |
| Central meridian | 6·zone − 183° |
| Scale factor k₀ | 0.9996 |
| False easting | 500 000 m |
| False northing | 0 m (N), 10 000 000 m (S) |
| Units | metre |
| Axis order | Easting, Northing |
EPSG codes
For WGS 84, northern zones are EPSG:326zz and southern zones EPSG:327zz, where zz is the zone number; for example EPSG:32637 is WGS 84 / UTM zone 37N. UTM is also defined on other datums, for example Ain el Abd / UTM zone 38N (EPSG:20438) and KSA-GRF17 / UTM zone 38N (EPSG:9358). The datum matters: the same latitude and longitude gives different eastings on different datums.
Scale factor and distortion
Because k₀ = 0.9996, distances on the central meridian are shortened by 400 ppm (40 cm per km). Scale reaches 1 about 180 km from the central meridian and about 1.0010 at the zone edge near the equator. Surveyors convert ground distances to grid distances with the combined scale factor.
Common mistakes
- Using the wrong zone: the same point in an adjacent zone has completely different eastings.
- Omitting N/S: a southern-hemisphere northing read as northern is 10 000 km wrong.
- Treating WGS 84 UTM and a local-datum UTM as identical.
- Swapping easting and northing columns on import.
- Applying a zone outside its 6° band: allowed for continuity, but distortion grows quickly beyond the zone edge.
Worked example
Convert Riyadh, 24.7136° N, 46.6753° E (WGS 84), to UTM.
| Datum / CRS | EPSG | Easting (m) | Northing (m) | Difference from WGS 84 |
|---|---|---|---|---|
| WGS 84 / UTM 38N | 32638 | 669,459.622 | 2,734,271.672 | — |
| KSA-GRF17 / UTM 38N | 9358 | 669,459.841 | 2,734,271.879 | 0.30 m |
| Ain el Abd / UTM 38N | 20438 | 669,525.211 | 2,734,259.173 | 66.8 m |
| WGS 84 / UTM 37N (wrong zone) | 32637 | 1,277,820.526 | 2,755,104.842 | different zone |
Try it in the Lat/Long to UTM converter.
Step by step
- Find the zone. Compute floor((lon + 180)/6) + 1 and check for the Norway/Svalbard exceptions.
- Choose the CRS. Pick the EPSG code for the datum and hemisphere, e.g. EPSG:32638 for WGS 84 zone 38N.
- Transform. Enter longitude and latitude (or easting and northing) in the converter.
- Check. Confirm easting is between about 160 000 and 840 000 m and the point plots in the right place on the map.
FAQ
How many UTM zones are there?
Sixty, each 6° of longitude wide, numbered 1 to 60 eastward from 180°.
What is the false easting in UTM?
500 000 m, so that all eastings in a zone are positive. The central meridian has easting 500 000 m.
Why is the scale factor 0.9996?
Reducing scale slightly on the central meridian spreads the distortion so that it stays within about ±0.04% across most of the zone.
Is UTM the same as WGS 84?
No. WGS 84 is a datum (and a geographic CRS); UTM is a projection. “WGS 84 / UTM zone 38N” combines both.
Which UTM zone is Saudi Arabia in?
Zones 36N to 40N. Most of the populated centre, including Riyadh, is in zone 38N; Jeddah and Makkah are in 37N; the Eastern Province is in 39N.
Related tools and articles
Tools
- Lat/Long to UTMConvert geographic coordinates to UTM.
- UTM to Lat/LongConvert UTM eastings and northings to latitude and longitude.
- Coordinate TransformationConvert between EPSG coordinate systems.
- Batch Coordinate ConverterTransform CSV or Excel point lists.
Articles
- UTM Zones: Find the Right Zone and EPSG CodeThe UTM zone of a point is floor((longitude + 180)/6) + 1, and its central meridian is 6·zone − 183°. In the M…
- Transverse Mercator ProjectionThe Transverse Mercator (TM) projection wraps a cylinder around the Earth touching a chosen central meridian. …
- WGS 84: World Geodetic System 1984WGS 84 is the global geodetic reference system used by GPS. It defines an ellipsoid (a = 6 378 137 m, 1/f = 29…
- KSA-GRF17: Saudi Arabia Geodetic Reference FrameKSA-GRF17 is the national geodetic reference frame of Saudi Arabia, defined by GEOSA and aligned to ITRF2014 a…
- Distance Reduction: Slope to Horizontal to GridA total station measures a slope distance. Surveys on a map projection need the grid distance: first reduce sl…
- EPSG:4326 (WGS 84 Latitude/Longitude)EPSG:4326 is the WGS 84 geographic coordinate reference system with coordinates in decimal degrees. The EPSG d…
References
- NGA. The Universal Grids and the Transverse Mercator and Polar Stereographic Map Projections, NGA.SIG.0012.
- Snyder, J. P. Map Projections: A Working Manual, USGS Professional Paper 1395, 1987.
- IOGP. EPSG Geodetic Parameter Dataset, epsg.org.
- IOGP. Geomatics Guidance Note 7-2: Coordinate Conversions and Transformations including Formulas, IOGP Report 373-7-2.
Cite this page
GeoCAD Bridge. “UTM Coordinate System Explained.” GeoCAD Bridge Knowledge Center, updated 2026-10-05. https://www.geocadbridge.com/knowledge/coordinate-systems-utm/