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How do I convert MGRS to UTM without doing the formula?

Set Primary to MGRS and Secondary to UTM in FieldGrid and the Map tab shows your position in both, one above the other, so there's nothing to convert. For a grid someone hands you, save it as a waypoint and switch the primary format to UTM: 13SDD 7594 2180 becomes 13N 475940 4321800.

3 min read · Updated 2026-09-23

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Your own position: two lines, no maths

  1. On the Map tab, tap the gear at the top. In Settings, find Coordinate format.
  2. Set Primary to MGRS and Secondary to UTM.
  3. Back on the map, the big line is your grid and the small line is the UTM for the same fix.

Standing at 39.04500, -105.27800 the top line read 13SDD 7594 2180 and the line under it 13N 475943 4321807.

To go the other way, tap the small line, or tap the UTM chip under it. The formats swap, so UTM is on top. That matters because tapping the big line copies it and pressing and holding shares it, and both take whatever is on top.

A grid you were given

A grid comes over the radio or in a message, and the map sheet in front of you only has UTM numbers in the margin. This is the case a converter is for.

  1. Open Waypoints, tap +, and switch the selector at the top of the sheet from Position to Manual.
  2. Type the grid in Coordinate. Spaces are optional, so 13SDD75942180 works too.
  3. Tap Save.
  4. Switch Primary to UTM. The waypoint's row now reads 13N 475940 4321800. Press and hold the row to copy it.

Converting back might seem to give 475943 4321807 again, but it instead gives 475940 4321800. That isn't a bug: an 8-digit grid names a 10 m square, and FieldGrid converts its south-west corner, so the last digit of each UTM number comes out as 0. Give it a 6-digit grid, 13SDD 759 218, and you get 13N 475900 4321800.

Doing it by hand, so you can check the app

Zone, easting and northing are shared between the two. MGRS swaps the leading digits for letters. Same point, taken apart:

13N 475943 4321807 to MGRS, step by step
PieceRuleResult
ZoneSame number in both13
Band letterFrom latitude, 8° bands; 39.045° N falls in 32-40° NS
Column letterZone 13 uses A to H; 475943 is in the 4th 100 km columnD
Row letterZone 13 uses A to V; 4321807 m is row 43, and 43 counts round the 20 letters to the 4thD
Easting digitsDrop the 100 km digit, keep 4: 759437594
Northing digitsDrop the hundreds of km, keep 4: 218072180

The digits are cut, not rounded: 75943 becomes 7594, never 7595. Going back the other way you need the band letter to decide which 2,000 km cycle the northing sits in. Band S runs from about 3,540,000 to 4,430,000 m north, and 4,321,800 is the only number ending in 21800 inside that, which is how 21800 turns into 4321800.

Where it stops

  • No UTM input. You can't type 13N 475943 4321807 into FieldGrid; manual entry and GOTO take MGRS or decimal lat/long only. For a typed UTM, use the table above or convert it to lat/long first.
  • The UTM N or S after the zone is the hemisphere, not the MGRS band letter. In this example the UTM says N and the grid says S, and both are right.
  • Each saved conversion takes a waypoint slot: 5 free, one more per optional ad, unlimited with Pro.
  • Grids show at 8 digits only. Type 10 and it accepts them, but shows 8 back.

Questions and answers

Is UTM the same as MGRS?
Same projection, same zones, same metres. UTM writes the full easting and northing, like 13N 475943 4321807. MGRS adds a latitude band letter and two letters for the 100 km square, then shortens the numbers: 13SDD 7594 2180.
What is the MGRS to UTM formula?
Turn the column letter back into hundreds of km of easting, the row letter into hundreds of km of northing, add the digits, then pick the 2,000 km cycle that matches the band letter. The worked table on this page goes through each step for one real point.
Can I convert UTM to MGRS in FieldGrid?
For your own position, yes: both formats show live on the Map tab. For a UTM someone gives you, no, because the app does not accept UTM as input. Do it by hand with the steps above, or turn it into lat/long and type that.
Why does my converted UTM end in a zero?
An 8-digit MGRS grid is only good to 10 m, so the app converts the corner of that 10 m square. The UTM it returns ends in 0 in both easting and northing.

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