6, 8 and 10 figure grid references explained
Every extra pair of digits in a grid reference makes it ten times more precise. Here is the same point, the summit of Snowdon, written at each precision:
| Figures | Example | Square size | Typical use |
|---|---|---|---|
| 4 | SH 60 54 | 1 km | Naming a grid square on a map |
| 6 | SH 609 543 | 100 m | Walking, route cards, DofE |
| 8 | SH 6098 5437 | 10 m | GPS positions, finding a specific feature |
| 10 | SH 60986 54376 | 1 m | Surveying, data and mapping |
A grid reference is a square, not a point
A 6-figure reference doesn’t mean one exact spot. It means “somewhere inside this 100 m square”. The reference is the square’s bottom-left (south-west) corner, and the area it covers stretches 100 m east and 100 m north from there. That is why references are truncated rather than rounded. Rounding up would name the wrong square.
When you enter a short reference in the converter, it places the pin in the middle of the square, because that is the best single guess.
Which should I use?
6 figures for most walking
On a 1:25,000 or 1:50,000 map you can comfortably estimate tenths of a grid square by eye, and 100 m is enough to find a path junction, summit or campsite. Route cards and most outdoor instructions expect 6 figures.
8 figures when you have GPS
A phone’s GPS in open country is usually accurate to between 3 and 10 metres, which matches an 8-figure reference. If you are reading your position from a phone or GPS unit, 8 figures passes on that precision without pretending to more.
10 figures for data and emergencies
Ten figures go down to 1 m. That is more than a handheld GPS can truly measure, but nothing is lost by giving the extra digits. In an emergency, read out whatever your device shows. If you’re unsure of the digits, 8 figures read clearly beats 10 figures read wrongly.
Turning one into another
To shorten a reference, drop digits from the end of each half, never just from the end. SH 60986 54376 becomes SH 6098 5437 (8 figures) and then SH 609 543 (6 figures). To lengthen one you have to measure again: adding zeros (SH 60900 54300) only names the corner of the original square and adds no real precision.