Live grid reference
Your position across three big lines — 100 km square letters, eastings, northings — updating as you move, truncated to the square you are actually in.
Ordnance Survey National Grid · OSGB36
Know exactly where you are.
Grid Reference turns your phone’s position into an Ordnance Survey grid reference — NN 166 712 — updating live as you move, spelled out in NATO phonetic, precise to the metre if you want it. It works offline, and your location never leaves your phone.
6 fig · 100 m
8 fig · 10 m
10 fig · 1 m
Everything you need to say where you are
NATO phonetic
The square letters are spelled out underneath — NN becomes NOVEMBER NOVEMBER — so you can read a reference aloud without anyone mistaking M for N.
Pick your precision
6 figures for 100 m squares, 8 for 10 m, 10 for 1 m. The footer always shows the grid in use: OSGB36.
Where you are, in words
A line under the reference names the nearest feature the Ordnance Survey way: in Sheffield, on Church Street, or 120m south east of Pennine Way.
Honest about signal
Lose GPS and the last reference stays on screen, dimmed, with a Signal lost banner and a live timer showing how out of date it is.
Copy, and follow the light
One tap copies the reference to the clipboard. Light and dark appearance follow your system setting.
How the reference is made
All the maths lives in one pure-Kotlin module, unit tested against the Ordnance Survey’s own worked example and cross-checked against an independent implementation.
01
WGS84 → OSGB36
GPS speaks WGS84; British maps are drawn on OSGB36. A 7-parameter Helmert transformation bridges the two datums.
02
Project to the grid
OSGB36 latitude and longitude go through the National Grid Transverse Mercator projection to become eastings and northings in metres.
03
Letters and figures
Eastings and northings become the 100 km square letters plus figures — truncated, never rounded, to the square that contains you, as the Ordnance Survey intends.
NN
November November
166712
Six figures place you inside a 100 m square — the classic hillwalkers’ reference. Switch to 8 or 10 figures for 10 m or 1 m precision.
Accuracy note: the Helmert datum shift is good to roughly ±2–5 m against the official OSTN15 transformation — immaterial at 6 figures, worth knowing at 10. Outside the National Grid — roughly, outside Great Britain — the app says so plainly.
Built to work with nothing
The “where you are” line is answered from map-label packs that live on your phone. Queries are always local — even in a dead zone, even months after the last download.
Downloaded once, used forever
A pack is fetched the first time you enter its region and cached on-device. Every query after that is answered instantly from the cache.
Refreshed politely
A pack older than a month is replaced quietly in the background — and only when your battery is above 50% or the device is charging.