How to find a National Grid Reference

When recording artefact data on our site, the location of discovery is extremely important. X marks the spot, and without this detail, the data we get is pretty useless to most archaeologists. Our database works on the OSGB National Grid system, and we convert these coordinates into Latitude and Longitude upon data entry, so that they can be redisplayed on web mapping systems.

In an ideal world, all finders would have a handheld GPS device, and would log a 12 figure grid reference at the time of finding an object. Obviously we know this is not possible for everyone, as such below are some tips on how to get a National Grid Reference (NGR). 

Below, we discuss the method to employ when you don't have a GPS unit:

  1. When you find an object, place it in a bag and write on the location of the findspot. This can something as simple as which corner of the field you are in or if it is next to a footpath. All this information will help pinpoint the grid reference later.
  2. Look at a 1:25000 scale OS map. There are a number of OS maps for each county, so you need to locate the one for the area in which your object was found. If you do not have copies of the OS maps, your local library will have them.
  3. Locate the findspot on the map, and then read the National Grid Reference; the first part will be the prefix (2 letters). The country has been divided into 100 km x 100 km squares, each with its own code e.g. Kent is TR or TQ. Each 100km square is then divided into 10km, each 10km square is divided into 1km and so on down to 10cm (this would be a 12 figure grid reference). We ask that you provide a 6 figure grid reference as a minimum, this means the location is pinned down to a 100m square. A lower figure than this is pretty useless for most archaeological research!
  4. The numbered grid on an OS map will give you a 4 figure NGR, so you will have to measure from the grid lines to the findspot to get 6 figures. Read the easting (across) first, and northing (up) second. If the findspot is on the grid lines, the third number of the easting or northing will be 0. The quickest way is to use the corner of a compass, as long as the scale is the same as the map used. See the picture below:
    Using a ruler to take a grid reference
  5. Make a note of the parish as well as the NGR.

Obtaining grid references online

There are websites that can provide the same information as an OS map. It just depends how you like to work, but the websites can be more accurate and clearly require less desk space. Good sites to visit to obtain NGRs are:

Using Magic for information on grid references

Magic Map is an interactive map service, that provides information on things like boundaries, historic sites and environment and is a DEFRA backed service. There have been rumours about this service closing, but it is believed that these functions will be consolidated elsewhere.

To obtain grid references follow these steps:

  1. From the Magic Map home page, click on the Interactive Map button
    The home screen for Magic
  2. From the drop down menu choose 'Administrative Areas' 
    Choose the admin areas
  3. Choose Place and type in the name of the place, or nearest place, where you found your object 
    Add the place name
  4. Make sure you read and agree to the terms of use. Click Open Map. 
  5. A new window will open. The first thing you need to do is zoom in on the map. We recommend you change the scale to 1:10000. You will be able to see buildings and fields at this scale. Click go, this will reload the map.
    Map of search
  6. From the top tool bar you need to choose the 'site check point' tool
    The site options bar
  7. This will open a new window. (Their accessibility is a bit low....) Type ‘10’ for the search radius meters. You can type anything, but this is a sensible value. Click next.
    Site check radius
  8. Another window will open, asking you to click on your search point on the map. You need to click on the map where you found your object, or as close as possible.
    Click on the search point
  9. If you cannot see your findspot, you can move the map around using this tool. Click on the hand, then click on the map. Holding down the left mouse button you can scroll around the map until you find the correct location.
    Details pane appears
  10. Once you have clicked on your findspot a final window will open (there may be a short delay),
    which provides the information needed. At the top in red is the 6 figure grid reference, with prefix
  11. This can be used to check the parish as well. If you scroll down the newly opened window you will find the district and parish.
    Final details 

Using wheresthepath

The Wheresthepath website provides some amazing functions, which you can use easily for obtaining grid references. You have the option to display Ordnance Survey maps (current and an out of copyright version) side by side with an array of layers on a Google map and overlay various types of grid. By clicking on the map, you get taken to a street map page as well.

To find a grid reference (and also latitude and longitude), follow these steps:

  1. Type place name into the search box and press enter
    Search text
  2. This brings up a dropdown list of places from the OS geocoder
    Geocoder enabled
  3. Choose the correct location
    Correct place chosen
  4. You can now start marking points on the map. In the bottom left corner, look for an icon with 4 points and 3 lines connecting them (labelled start entering route nodes when you mouse over)
    Select tool
  5. Click this and then click at a point on the map where you found an object. This puts a  circle on both maps (green for the first point) and if you add more, it links these points up with a line.
    Selected point in green
  6. To obtain the NGR for each of these points you have clicked, click on the printer icon and a new window appears with a map showing your points and a list of the NGRs (10 figure)
    Printout marked up with NGRs

The example below shows Maiden Castle, a rather famous Iron Age hillfort in Dorset, excavated by Pitt-Rivers and subsequently by Niall Sharples (more info on this amazing place can be found on wikipedia). Obviously, metal detecting or any form of invasive work cannot be performed on this scheduled monument.

A small screen shot of the Maiden Castle on where's the path

Using Street Map

Street Map is an online mapping service, that provides information on street, building and environment locations. It can also be used to generate grid references for use on our website. To obtain grid references from Street Map, follow these steps:

  1. From the Street Map home page click on 'place' and type in the name of the place, or nearest place, where you found the object. Click 'go'.
    Place entry window
  2. You can move the map around to locate the findspot using the arrows at the side and top. You can zoom in and out using the controls at the side.
  3. When you can see your findspot, click on 'move arrow' on the right side, and click on the map where the object was found.
    Move arrow icon
  4. Then click on 'click here to convert coordinates' at the bottom of the map.
    Convert coordinates tab
  5. This will open a new window which will display the required information. The NGR with letter prefix is next to the heading ‘LR’.
    Conversion window


The webservice is perhaps best used for converting coordinates or looking up coordinates from postcode. Some of the time, our finders bring finds in with coordinates in latitude and longitude. Our database converts from Grid reference to Lat/Lon pairs and not the other way round at the moment. We also produce a Yahoo Where on Earth ID and elevation of the findspot from the geonames service.

This example shows how to convert a Lat/Lon pair to National Grid:

  1. Go to the coordinate converter box and enter your Lat/Lon pair and hit enter.
    The coordinate converter
  2. Once refreshed, scroll down the page and look for the OSGB grid ref and a map. Below this is series of form fields: X & Y coordinates, easting/northing, full grid ref, 6 figure, 4 figure, grid square. The Scheme wants the full grid reference for the database.
    Converted coordinates