UK Grid Reference Finder

Surveyor.DEV

About this app

Turn your GPS position into a British National Grid reference, and convert between every coordinate system used in Britain and Ireland. It all works offline, on the phone, with no signal at all.

Free. No ads. No accounts. No tracking.

An independent app, not affiliated with Ordnance Survey or any government body.

GRID REFERENCE FINDER, POSTCODE FINDER, COORDINATE CONVERTER

Your position, in every format at once:

• OS National Grid reference, 2 to 10 figures
• OSGB36 easting and northing
• WGS84 latitude and longitude, in decimal degrees, degrees and minutes, or degrees minutes seconds
• MGRS, the system used by NATO and mountain rescue
• Plus Codes (Open Location Code), as used by Google Maps
• Irish Grid reference, and Irish Grid easting and northing
• UK postcode

Every one works both ways, and anything the app shows you, you can type back in: with N/S/E/W at either end, a plus or minus, or neither. Paste a pair from a spreadsheet or a message and it splits itself into the right fields.

Show only the cards you use, drag them into the order you want, set the precision of each, and tap and hold any value to copy it.

WHY IT IS ACCURATE

Most apps convert with a 7 parameter Helmert transformation, which is good to roughly 5 metres across Great Britain.

This one uses Ordnance Survey's own OSTN15 model, built into the app rather than downloaded:

• 0.15 m horizontal accuracy at 95%, and 0.148 m measured against OS's own published test points
• Proper OSGB36 values, not an approximation
• True 10 figure grid reference precision

The Irish Grid uses the official OSi and Land and Property Services polynomial.

A COMPASS THAT MATCHES YOUR MAP

Most compass apps show magnetic north and leave the corrections to you. This one shows all three norths at once:

• Magnetic, what the sensor reads
• True, corrected using the World Magnetic Model from your position
• Grid, the north your OS map is drawn against, using the exact grid convergence where you are standing

Tap the dial to mark a bearing and the app shows which way to turn back. A spirit level shows when the phone is flat enough to trust the reading.

POSTCODE FINDER, ONLINE AND OFFLINE

Postcodes come from postcodes.io when you have a connection. With no signal the app falls back to the device geocoder, so you still get an answer in the field.

IN YOUR OWN LANGUAGE

Fourteen languages, Welsh and Irish among them. Every screen, not just the menus, with the surveying terms translated as surveying terms.

PHONES AND TABLETS, EITHER WAY UP

Turn the device and the layout follows: two columns sideways, three on a tablet. Or lock it to portrait or landscape, for a dashboard or handlebar mount.

MADE FOR FIELD USE

• Works offline, indoors or outdoors
• Left or right handed button placement
• Dark mode, haptic feedback, adjustable GPS rate
• Share your position as text, open it in your maps app, or open it on the MapGrid web map with a named marker

Built for hillwalkers, mountain rescue, surveyors, ecologists, GIS and archaeology professionals, geocaching, hiking and anyone who has ever read a six figure grid reference over a radio.

SOURCES AND DISCLAIMER

UK Grid Reference Finder is an independent app by Surveyor.DEV. It does not represent, and is not endorsed by, Ordnance Survey, the UK Government or any other government body. The official data it uses comes from these sources:

• OSTN15, OSGM15 and OS Open Names, Ordnance Survey: https://www.ordnancesurvey.co.uk
• Irish Grid polynomial, Tailte Éireann (formerly OSi): https://www.tailte.ie and Land & Property Services: https://www.finance-ni.gov.uk/land-property-services-lps
• World Magnetic Model, NOAA/NCEI and BGS: https://www.ncei.noaa.gov/products/world-magnetic-model
• Postcodes, postcodes.io: https://postcodes.io, using Office for National Statistics data: https://www.ons.gov.uk

Contains OS data © Crown copyright and database right 2026.

What’s new

🆕 New since 3.2.0:
• Plus Codes can be shown the way Google Maps writes them, with a nearby town: FVVP+P4 London. Switch it on in Settings › Grid Formatting › Plus Code
• Manual input now accepts short Plus Codes, with or without a town after them
• The OS Grid Reference card shows the size of square it names: 6 figures, 100 m squares