Map reading skills: How to read a grid reference

On week four in our six-week blog series on map reading skills, we’re taking a look at how to read a grid reference. Map reading is an essential skill for any explorer or outdoor enthusiast. We’ve teamed up with Steve Backshall to record a series of videos to remind you of the basics and help you feel confident with your map.


So far we’ve covered which OS map you needunderstanding map symbols and making sense of contour lines. Today we’re covering grid references, both four-figure and six-figure version. Over the next fortnight we’ll also cover:

  • Knowing your compass and how to take a compass bearing
  • Understanding magnetic north

Each week we’ll share Steve’s video with you, give a summary in the blog and point you in the right direction of further resources and details. Hear what Steve has to say about grid references in these two short videos:

Why do we need to know how to read a grid reference?

As Steve said, it really could save a life. Our and about in urban Britain, if you spot an accident and call the emergency services, chances are that you’ll be able to give an address, street name, postcode etc. But if you’re out walking and you fall and injure yourself – it is unlikely that you will know the postcode of where you have fallen. If you’re able to provide six figure grid reference of where you are that narrows your location down to a 100 metre square box and could make a huge difference to how quickly the emergency services can get to you.

How to read a four-figure grid reference

Whether you are using an OS Explorer Map (the orange ones) or an OS Landranger Map (the pink ones) you’ll notice that the map is covered with a grid of thin blue lines that form square boxes all over the map.

Each line, whether running vertically or horizontally across the map has a number on it (both at either end of the line and somewhere halfway along).

The numbers that run from left to right (or west to east) on the map are called Eastings – this is because the number of the line increases the further east you go.

The numbers that run from bottom to top (or south to north) on the map are called Northings – this is because the number of the line increases the further north you go.

IMG_3818Using OL13 for the Brecon Beacons as an example, imagine we are following the Three Castle Walk near its crossing with Bont Brook and want to let people know where we are. To take a four figure grid reference you take the Easting first (taking the number that is bottom left of the square you are looking for) and then the Northing. Regardless of which map you are using – this places you in a 1 km square box, in this case, 3920.

IMG_3817Great Britain is also broken down into 100 km square boxes – each has a prefix of two letters. These letters can be found in each of the four corners of your map. Add these to the start of your grid reference and you have pin pointed your exact location. In this case, we’re in square SO, so our four figure reference is SO3920.


How to read a six-figure grid reference

If you want someone like the emergency services or mountain rescue to come to you quickly – you’ll want to narrow down the area by creating a six figure grid reference – this will then place you in a 100 metre box.

What you need to do is imagine that that one box identified in your four figure grid reference is broken down into smaller squares – 10 x 10 squares, which are marked all around the edges of your map.

Starting with “0” as the number of the first box – count across from the Easting line to where you are and add this to your Easting number of your four figure grid reference.

Then you do the same with the Northing – starting with “0” in the first box – count up how many squares you are from the bottom northing line of the square.

Putting these together you have your six figure grid reference so this puts us at SO393203.

You can download our map reading booklet or map reading made easy peasy (aimed at children) that take you through how to take a grid reference with more examples. So that’s it – my lesson on how to take a grid reference is over. Now you can take to the hills and be able to tell someone where you are!

Happy exploring! I’ll be back next week to talk about how to use a compass.

You may also like

National Map Reading Week coming in October
When GPS fails…could you navigate with a paper map and compass?
Stay safe and brush up on your map reading skills
Map reading skills: What is magnetic north?

27 Responses

  1. Unfortunately grid references are no use when your map is folded to show only the area you want…and it’s inside your map case. Grid references are fine when you’ve got a table to fully unfold your map on a desk, and it’s nice and warm inside…pretty useless on a day like today out on the moors when it’s cold, wet, and windy.

    1. Alan

      If my map is going to be folded, I always write the grid numbers onto the visible area. Only takes seconds and job done.

  2. James

    Lee,just remember to take the grid refrence before you go on your trip so if you get lost atleast you will know where you are

  3. Kickaha Wolfenhaut

    I’m sure the grid numbers used to be printed occasionally across the map itself. Not so many as to smother the map, but enough so that you could see them however you folded it.
    Sad to say that my first purchase in many years is bitterly regretted as this is no longer the case. Writing the numbers on yourself is a workaround – but a workaround for a daft omission on the part of O.S.

    1. Hi

      Thanks for getting in touch. I’ve passed your feedback along to the Product team and they advised that on OS Landranger maps internal grid figures changed to set intervals and are shown on each panel of the folded map. This is due to a change (from 2015) in the Landranger specification which will be rolled out to all titles in the range as they come up for revision. For OS Explorer maps, grid figures are shown on each 10km line, this has been the case since 1995.

      Many thanks

  4. Hii which side are started in reading a grid refference also which line are started to read and how to use the scale in calculating the area of map.

  5. Steve Bennett

    Sloppy description. “The lines that run from left to right (or west to east) on the map are called Eastings – this is because the number of the line increases the further east you go.” A line from west to east has the same number no matter how far east you are along it. The numbers on the north-south lines increase.

    1. Alex

      Thanks for pointing it out Steve – I mean, this is the Ordnance Survey website.
      I thought I was cracking up until I read the posts at the bottom of this page.

      The description still has not been ‘corrrecctedd’: –
      The lines that run from left to right (or west to east) on the map are called Eastings – this is because the number of the line increases the further east you go.

      The lines that run from bottom to top (or south to north) on the map are called Northings – this is because the number of the line increases the further north you go.

    2. Jason

      The confusion is in your minds. Gemma’s discription is correct.

      Grid systems vary, but the most common is a square grid with grid lines intersecting each other at right angles and numbered sequentially from the origin at the bottom left of the map. The grid numbers on the east-west (horizontal or x) axis are called Eastings, and the grid numbers on the north-south (vertical or y) axis are called Northings.

  6. Hi
    For many years most Caravan Centres (of the Caravan Club of Great Britian) have used the Landranger Map No and the 6 digit reference code. (e.g. 150 737371) This allows members to buy the correct Landranger map series and then use the 6 digit reference to find the location. However you cannot use this reference type in any online mapping system that I’m aware of. You need to convert the map number to the grid ref (e.g (Landranger Map 141 contains some of grid reference SK and some of SP) Most online mapping systems will quote the SP reference, my question is: is there an easy way to find the Landranger map number from the grid reference number?

    1. Hi Mick

      It’s a good question and we’ve passed the feedback along to our development team. Most GB online mapping systems will use OS grid references to locate a position, however the standard OS paper sheets were around prior to online services, and we haven’t a current system to link the two.

      One thing that might be of some assistance is a feature of our OS Maps online service, http://www.os.uk/osmaps. If you do a grid reference search using the grid reference icon, it returns a grid reference. If you then click on “buy a Paper Map”, the link takes you to our website which lists the paper maps that are relevant for that location. I hope that will be of some use.

      Many thanks

      1. Phil

        Gemma, contrary to your description, as far as I’m aware the horizontal lines are called northings and the verticals are eastings.

  7. Barney

    None of my maps have grid references. in fact they are quite barren. They just look like a vast expanse of snow.

  8. hi this website has been really useful but on my homework it saysfind the post office at south south west. I don’t no how to find out south south west. can you please tell me.

    1. hi this website has been really useful but on my homework it saysfind the post office at south south west. I don’t no how to find out south south west. can you please tell me.

  9. Ross

    Hi Gemma
    I am trying to find out the official name of the letters used in the OS grid reference, We have Easting and Northing which covers the 10K down to 1metre and less but I cannot find a Name for the “N” 500K square or the “NN” 100k square the best I can come up with is letter pair. It would seem all descriptions skirt around the issue where it would be very helpful to have a term to describe these squares.

  10. Pingback : Introduction to Field Recording- Part 1 | Chris Kolonko

  11. Dr V Flook

    Reading through all these comments I just wonder what these people have been taught in school geography lessons. Several decades ago all children could read a grid reference in their early teens and work out the gradient profile of a planned walk and derive lots of other information from OS maps. The modern maps are still providing the information and it is still just as easy to read, it only the teaching in schools which has changed.

  12. Clive Beere

    About teaching that has changed in respect to reading OS grids. Yes , teachers are less focused on these skills today, but also students listen less adeptly. Also , today I taught a year 9 Geography class and I noticed a booklet on Map Reading. On looking at the explanation on how to read OS maps using 6 digit reference; I noticed that the examples were erroneous as one case listed locations that were not even on the map, and the grid reference for some of the problems did not even exist on the map sample. I do not see how it possibly could have been peer read and approved. Yet it had the logo in the top right cover page for the Independent Schools Exam Authority!!! Also they did not even show a couple of examples to let students decode and make sense of the 6 digit method, but only showed small fragments of an OS map and some of the 6 digit references did not even have all the Eastings and Northings on the example piece.

  13. Keith

    On the Suffolk CC website the locations of a footpath closure are given as 644470 256030 to 645610 255560. I have worked out that these are 10 figure grid references preceded by a 6 on the eastings number and a 2 on the northings number. Presumably these two figures identify the 100km square. Can anybody explain how to work out which 100km square is being referenced from these two numbers? The Landranger sheet number is 156.

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