How to Show UTM, Lat/Long and OSGB Coordinates at the Same Time on iPhone

TL;DR

Pick a primary format in Settings and tick up to two extras to show underneath. Supported: MGRS, USNG, UTM/UPS, lat/long (DD, DDM, DMS) and OSGB. The datum choice only changes latitude/longitude; the grids use their own standard datum.

The problem

The map says UTM, the radio operator says MGRS, the guidebook gives degrees-minutes-seconds, and a British map uses OS grid letters. Converting by hand is slow, easy to get wrong and impossible in the rain. And “which datum is that?” is the question that catches people out.

Set it up

  1. Go to Settings → Coordinate format.
  2. Choose the Primary format: MGRS, USNG, UTM/UPS, Lat/Lon (DD), Lat/Lon (DDM), Lat/Lon (DMS) or OSGB.
  3. If it’s MGRS/USNG, choose MGRS figures (2–10).
  4. Under Show with…, tick up to two extra formats. They appear below the main readout on Location, each tap-to-copy.
  5. For lat/long, pick the Datum for each slot.

Enter in one, read in another

When you add a waypoint, type its coordinate in your primary format (the field says which, for example “e.g. 38SMB 44880 11710”). Then change the primary format and the same point is shown in the new one. The map’s search box also accepts a typed grid or lat/long and jumps to it.

For MGRS, you can leave out the zone, or the zone and 100 km square: the app fills the rest from your current position. That’s handy for a short grid heard on the radio.

What the datum setting does (and doesn’t)

  • It changes latitude/longitude readouts and the lat/long you type in. NAD27 or ED50 coordinates read from an old map will line up correctly.
  • It does not change MGRS, USNG or UTM, which are always computed on WGS84, nor OSGB, which is computed on OSGB36. The app doesn’t offer a datum choice there, so there’s no false promise.
  • Each extra format has its own datum, so one screen can show WGS84 MGRS and a NAD27 lat/long.

Sanity check

Put the same waypoint into two formats and compare it against a known point (a trig pillar, a car park you know). If the answers disagree by tens or hundreds of metres, you’ve almost certainly got the wrong datum on a lat/long.

Limits

  • Polar regions (north of 84°N, south of 80°S) aren’t output as MGRS text; use UTM/UPS.
  • Not certified for surveying or aviation use.

FAQ

How many formats can I show at once? Three: a primary readout plus up to two extras underneath. Tap any of them to copy.

Which formats are supported? MGRS, USNG, UTM/UPS, latitude/longitude in decimal degrees, degrees-decimal-minutes and degrees-minutes-seconds, and OSGB (British National Grid).

Which datums? WGS84, NAD27, OSGB36, ED50 and AGD66. In this version the datum changes latitude/longitude readouts. MGRS, USNG and UTM are always on WGS84 and OSGB is always on OSGB36.

Can I convert a coordinate someone sent me? Yes. Type it in when adding a waypoint (or in the map search) and read it back in any other format.

The app MGRS GPS →