British National Grid

The Ordnance Survey British National Grid is a grid referencing system for Great Britain. The grid references are used in conjunction with Ordnance Survey maps, but also with other maps and charts as well as some GPS-enabled mobile applications and GIS software.

How do I find a British National Grid reference?

Most commonly, British National Grid references are determined using the blue grid on the Ordnance Survey Landranger and Explorer maps. Firstly, there is a two letter prefix to determine the 100km grid square.

The subsequent numbers can be structured as 4-figure, 6-figure or 8-figure coordinates, depending on the accuracy required. A 4-figure reference can be obtained using the blue grid, eastings first (across) followed by the northings (up). A 4-figure reference is only accurate to the 1km grid square.

4-figure Grid reference example: SP 43 14

For improved accuracy (e.g. for specifying the location of a field), then a third figure for each of the eastings and northings should be estimated by dividing the grid square up further into an imaginary 10 x 10 grid creating 100m grid squares. This is used to determine a 6-figure grid reference and is the most widely used reference.

6-figure Grid reference example: SP 435 143

An eight figure grid reference would be accurate to 10 metres.

8-figure Grid reference example: SP 4357 1430

Examples can be found on the Ordnance Survey website.