MGRS Precision Table
4-digit: MGRS = [Zone][Square] [EE] [NN] (1,000 m precision)
6-digit: MGRS = [Zone][Square] [EEE] [NNN] (100 m precision)
8-digit: MGRS = [Zone][Square] [EEEE] [NNNN] (10 m precision)
10-digit: MGRS = [Zone][Square] [EEEEE] [NNNNN] (1 m precision)
Reference Table
| MGRS Digits | Example | Precision (Square Size) | Typical Use |
|---|---|---|---|
| 4-digit | 18S UJ 23 06 | 1,000 m ±1,000 m | Large-scale tactical planning |
| 6-digit | 18S UJ 234 064 | 100 m ±100 m | Standard military operations |
| 8-digit | 18S UJ 2348 0647 | 10 m ±10 m | Artillery/precision navigation |
| 10-digit | 18S UJ 23480 06470 | 1 m ±1 m | Engineering, EOD, survey control |
| 12-digit | 18S UJ 234800 064700 | 0.1 m ±0.1 m | High-precision survey (non-standard) |
Engineering Consequences
MGRS precision errors are common and can be dangerous in the wrong context:
- Wrong 100km square identifier: A single letter typo shifts the target by 100+ km, a well-documented cause of GPS-era navigation failures.
- Truncation: Truncating a 10-digit MGRS to 6-digit in software may appear harmless but enlarges target dispersion from 1 m to 100 m, unacceptable for precision operations.
- Datum assumption: MGRS is typically based on WGS84 in modern systems; historical maps may use NAD27 or local datums, shifting coordinates by 10 to 300 meters.
Frequently Asked Questions
Is MGRS always WGS84?
Modern NATO/US military MGRS grids are based on WGS84. However, topographic maps printed before the mid-1990s may contain MGRS grids based on local datums such as NAD27 or ED50. Using a modern GPS MGRS output to navigate on an old paper map without checking the datum can produce errors of 10, 00 metres.
What happens if I read an MGRS grid square letter wrong?
MGRS uses two letters to identify a 100,000-metre square within the grid zone. A single letter error, e.g., reading 'UJ' as 'VJ' —would shift the location by exactly one 100 km square (100,000 metres) in the east-west direction. This is one of the most operationally dangerous single-character errors in geospatial data handling.
Using the wrong datum or applying coordinates without grid-to-ground correction can cause 1-400 metre positional errors —a leading cause of surveying negligence claims and contract disputes.