dd mm.mmm

 dd mm





OS Grid





 dd mm.mmm

 dd mm


 OS Grid (numeric)

 OS Grid (trad)



 UK County (1974 boundaries)


 Accuracy (metres)


Single mode has one input box at the top. Enter any lat/long or OS Grid format, UTM or w3w. There are separate output boxes for each format.

Multiple mode has separate boxes for each format that serve as both input and output.

Single mode is easier to use, multiple mode is more flexible and allows more detailed error messages.


The most common UTM format uses latitude bands from C in the far south to X in the far north.

The latitude also partly specifies the band. If you supply a band that conflicts with the latitude, the program will use the latitude band only to determine the N/S hemisphere, and will warn you about the error.

The alternative to latitude bands is to specify the hemisphere using N/S. These examples are for Nelson's Column in London ...

Using latitude band - 30U 699312‍ 5710154
Using hemisphere - 30N 699312‍ 5710154


Adds degree, minute & second symbols to the DM & DMS outputs, and removes the comma separator from the D output.

v1.92 03/03/2023

Converts between different lat/long formats, OS National Grid formats, UTM and what3words.

Type or paste into the appropriate box and tap the button to the right of it. Examples:

dd mm.mmm ... N51 42.729 W000 24.853
dd mm ... N51 42 35.26 W000 24 54.82
dd.ddddd ... 51.75639 -0.43286

E & N are positive, W & S are negative. Use N, S, E, W, + and - prefixes or suffixes to specify the hemisphere (not required for E or N).

Degree, minute & second symbols are accepted in the appropriate places but are not required. For Degrees, use a comma or space separator, or a comma followed by a space.

OS Grid numeric format is 4 to 6 digits each for Eastings and Northings (7 for Northings in north of Scotland). You will be warned about low resolution if you use only 4 or 5. Traditional format is 2 letters followed by 3 to 5 digits each. Use a space to separate Eastings & Northings.

You can copy the output to the clipboard - select which format you want on the clipboard and tap the Copy button.

This program can use location services provided by your browser to populate the boxes. If you are asked to permit the web page to use your location you should, of course, allow it to do so. You should also use the https protocol instead of http, though the program will attempt to redirect you should you use http.

Location services on mobile browsers vary significantly in their behaviour. Some may return a low accuracy fix if a high accuracy fix is not available, even if high accuracy is requested. The reported accuracy is therefore displayed. If you enter co-ordinates manually, the accuracy is shown as 0 metres.

The accuracy shown is that reported by the phone's API. This is usually expressed as the 95% CEP (circular error probable) figure, i.e. the distance to which the location should be accurate 95% of the time. This should be the same method used by other apps on the same device.

The time taken to return the location is variable. If the GPSr is already powered up and in use by a native application, the browser should return immediately.

If the co-ordinates are in England, Scotland or Wales the page will display the county.

County boundaries change periodically. The program uses the 1974 boundaries because these are the only ones for which I have been able to obtain appropriate polygon data. I believe they are the same as those used by GSAK, but they are not the same as used by Project GC.

Sources of error include the resolution of the polygons and inaccuracies in the supplied location. The program will look beyond the immediate location to see if you are near a county boundary, and if so will warn you, as the result is less reliable. How near is "near" depends on the accuracy.

The what3words API may also report the county of the nearest town, and this may differ from the 1974 county.

Dumfries and GallowayDurham
DyfedEast Sussex
Greater LondonGreater Manchester
HampshireHereford and Worcester
HumbersideIsle of Man
Isle of WightKent
MerseysideMid Glamorgan
NorfolkNorth Yorkshire
NottinghamshireOrkney Islands
Scottish BordersShetland
South GlamorganSouth Yorkshire
TaysideTyne and Wear
WarwickshireWest Glamorgan
West MidlandsWest Sussex
West YorkshireWestern Isles