How to Convert Grid Reference to Coordinates

Written by donny quinn
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How to Convert Grid Reference to Coordinates
The Ordnance Survey grid provides less locational variation in Britain than coordinates. (Britain map image by NataV from

The Ordnance Survey, according to their website, created a grid for the United Kingdom in order to adjust for the inaccuracies in location due to two-dimensional flattening of three-dimensional globes. The curve of the Earth causes distortion when adjusted into a two-dimensional form (i.e., a map). In order to minimise location distortion within the United Kingdom, the Ordnance Survey (OS) created a grid system that allows for users to find a location by grid numbers, rather than coordinates.

Skill level:


  1. 1

    Select either Moveable Type or Obliquity below. Both of these programs provide conversion from OS grid references to latitude and longitude.

    Because conversion between OS grid references and latitudinal and longitudinal coordinates requires such an advanced mathematical formula and knowledge of trigonometry, it is often better to use computer programs that can convert for you.

  2. 2

    Enter your OS grid reference number.

    On Moveable Type, highlight the entire grid reference number in the middle of the page, press delete then enter the grid number you want to convert.

    On Obliquity, select the grid square from the drop-down menu, then enter the easting and northing. The easting is the first set of digits after the square number, while the northing is the second set of digits. For example, if your grid number reads "TG 514131" then out of the six numbers, the first three represent the northing while the second three represent the easting.

  3. 3

    Press "Enter" or select the button to convert. The latitude and longitude coordinates pop up.

    On Moveable Type, press "Enter."

    On Obliquity, select "Where is it?"

Tips and warnings

  • To translate from the OS grid system to traditional coordinates, it helps to understand how the OS grid system works. The OS grid system values contain three sets of information: two letters at the beginning and two sets of numbers following. The first letter represents a 500km square on the map of the United Kingdom. The second letter represents a 100km square within the first letter's 500km square. Each following number subdivides the 100km square, so that six total easting and northing numbers identifies a 100m square area, eight total numbers identifies a 10m square area and ten total numbers identifies a 1m square area.

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