Convert OS grid references to lat/lon coordinates

Modern smartphones and satellite navigation systems can provide assistance to help you with getting to the start or meeting point for one of our walking and climbing events. Here’s how.

We focus on two of the most common aids to help you – maps on smartphones and in-car satnav systems. We explain how to convert OS grid references to lat/lon coordinates.

Location information in our published programme of events usually consists of short descriptive information and an Ordnance Survey (OS) grid reference to look up on a map.

Maps on smartphones

The OS Maps app on smartphones is one assisted way to find the start point for one of our events. It’s free and works without needing a paid subscription for the OS map products.

Note: OSMaps is available for both Apple and Android smartphones.

Once you have the app open, enter a full grid reference, for example SN987198 in the ‘search for a location’ box in the app. Tap the grid reference displayed as the search result. This shows you a point on a map where you will see an option to ‘Get directions’. See the picture at the beginning of this article. Choose ‘Get directions’ and then choose your preferred standard map/navigation app – Google Maps, Apple Maps or Waze. Use that to obtain driving directions from wherever you’re starting from.

It’s important you include the two grid letters (‘SN’ in the above example) of your grid reference, otherwise the app can’t give you the location. It’s good (but not necessary) to use a 10-figure grid reference if you have one. These are more accurate than 6-figure references. They are especially useful for accurately locating features such as a small crag or parking spot, for example.

In-car satnav systems

In-car satnav systems are generally easier to follow when driving than apps like Google Maps or Apple Maps. So if you have an in-car system, whether factory-fitted or aftermarket add-on, its better to use this than a smartphone.

People who use in-car satnav systems will generally know that the usual method of setting them up is to enter a postcode and/or an address for the destination you want to drive to. This works well in urban areas where many destinations have a specific street address and postcode. It doesn’t work so well when you want to find a car park at the base of a remote mountain or a crag in the middle of a forest.

Most modern satnav systems can accept latitude/longitude (lat/lon) coordinates as input these days. Satnav systems use lat/lon coordinates because they work anywhere in the world.

We explain further below how to convert OS grid references to lat/lon coordinates. First though, what is latitude/longitude and how do you put it into your satnav?

What are latitude and longitude?

Latitude and longitude are part of the global geographic coordinate system. They’re expressed as degrees of a circle.

Lines of latitude range north from the Equator (0°) to the North Pole (90°N) and south from the Equator (0°) to the South Pole (90°S) .

Lines of longitude range in each direction East and West from the Prime Meridian in Greenwich (0°) until they meet at the 180° Meridian on the opposite side of the world. Longitude is expressed in the range 0° – 180°E and 0° – 180°W. 180°E and 180°W are both the same line of longitude.

A ‘lat/lon’ coordinate pair of numbers, such as 51.0°N, 3.0°W indicates a precise position on the surface of the Earth.

Putting lat/lon coordinates into a satnav system

In your satnav system, try looking beyond the option to enter an address/postcode. Look for an option to ‘enter coordinates’ or ‘enter latitude/longitude’. It may be elsewhere in the menus of your system. You might need to refer to the manufacturer’s usage instructions to find it. But it’s probably there somewhere.

You’ll need to know what format the device requires as input.

Two formats for lat/lon coordinates

Latitude and longitude (lat/lon coordinates) can be expressed either as decimal degrees or as degrees, minutes and seconds (dms). Here’s an example of each for the same location:

Grid Reference (6 figure): SN987198
Latitude , Longitude (decimal): 51.868345, -3.4722274
Latitude , Longitude (degs, mins, secs): 51°52′06″N, 003°28′20″W

Notice how decimal lat/lon uses positive and negative decimal numbers to indicate ‘north of the equator and west of Greenwich. The degrees, minutes and seconds (dms) form uses the letters N and W.

Normally, decimal lat/lon uses ‘plus’ (+) and ‘minus’ (-) signs to designate latitude North (+) or South (-) and longitude East (+) or West (-). Importantly for most gwentmc events, a longitude will mostly have a ‘minus’ (-) sign, meaning West of London/Greenwich. The dms lat/lon normally uses letters – ‘N’ or ‘S’ and ‘E’ or ‘W’ as in the above example.

However, this is not always the case! The author’s in-satnav car uses dms with ‘minus’ (-) signs for South and West. In the absence of minus (-), a ‘plus’ (+) sign is assumed for North or East.

When you know which format variation your device uses, it’s straightforward to enter the position of your intended destination. Then you ‘start guidance’ in the normal way.

Note: You can use decimal lat/lon in Google Maps and Apple Maps, instead of an address or place name.

Convert OS grid references to lat/lon coordinates

Here we explain two ways to convert OS grid references to lat/lon coordinates.

Using OS Maps app

Convert a grid reference to lat/lon using the OS Maps app in several steps, as follows:

  1. Find the location you want to travel to, either by entering a grid reference as described above or by finding and then touch/hold the location on the map until the marker appears.
  2. Then choose ‘Get directions’ followed by ‘Copy GPS Coordinates’. This will copy the coordinates to the clipboard of the device on which you’re using OS Maps.
  3. If your satnav uses decimal lat/lon, do the following:
    • Open a Notes app, start a new note and paste into the note. Then you’ll be able to see the lat/lon coordinates extracted from OS Maps. For example, for grid reference SN987198 you will paste 51.867553938641144,-3.472662361466499.
    • Reduce each coordinate of the pair to six or five decimal places i.e., 51.867553 and -3.472662. Enter these numbers into your satnav. That’s all you need to do. Now ‘Start guidance’.
  4. If your satnav uses dms lat/lon, do the following:
    • Open Google Maps and paste into the search box. For example, for grid reference SN987198 you will paste 51.867553938641144,-3.472662361466499 and will see this in the search box.
    • Tap ‘Search’. You’ll see the location displayed with the dms lat/lon shown alongside and also in the white part of your screen. For the above example: 51°52’03.2″N 3°28’21.6″W.
    • These are the numbers to use for your satnav. You may need to use a minus (-) sign instead of W(est). You may also need to round the minutes down or up i.e., 03.2″ becomes 03″ and 21.6″ becomes 22″. That’s all you need to do. Now ‘Start guidance’.
Using Gridreference Finder

Another way to convert OS grid references to lat/lon coordinates is to use the Grid Reference Finder website (

This works best on a tablet, laptop or desktop PC. It works on a smartphone too but is a bit more fiddly because of the small screen size.

First, open the browser (Safari, Chrome, Firefox, etc.) on your phone and enter the website address: You can set this up as a shortcut or favourite to make life easier.

Then enter your grid reference in the appropriate box on the left side and press ‘Go’, as shown below.

You’ll see a panel appear with lat/lon coordinates in both decimal and dms forms. Use whichever is appropriate for your satnav system, perhaps including using a minus (-) sign instead of W(est). We’d advise against using the postcode. It will probably lead you to a destination some distance from where you actually want to be!

Note: Gridreference Finder offers a number of other useful pieces of information and options.

More detailed location information for our events

OS grid references are the principal way we specify location information for our upcoming events. These are always at least ‘6-figure’ references. They consist of two grid letters designating the relevant 100km grid square, followed by six grid digits identifying a location within that 100km grid square. This provides accuracy within 100m, which is usually sufficient to find the starting or meeting point for an event. On occasion, where greater accuracy is helpful we will provide a ’10-figure’ grid reference (i.e., accurate to 10m). as well.

Increasingly, we publish details of our meeting points as standard ‘venues’ in our events calendar. When you look at the event details, such as this recent walk up Pen y Fan, the venue shows as a clickable link to more information – as in the image below.

For climbing events, we provide a link to relevant crag information page on the UKC (UKClimbing) website; for example, Tirpentwys. You can find an OS grid reference for the crag on the Map tab. Access directions are on the Overview tab.