Decimal Places in Coordinates: What Precision Means

Each decimal place in a latitude or longitude shrinks the possible area by a factor of ten. With no decimals you are within roughly 111 km, with four you are within about 11 m, and with five you are down to about 1.1 m. Beyond six decimal places, the numbers describe less than a centimetre or so and are usually beyond what any phone can measure.

The table

These values are for latitude, where one degree is about 111 km everywhere:

Decimal places	Example	Approximate resolution
0	41	111 km
1	41.4	11 km
2	41.40	1.1 km
3	41.402	110 m
4	41.4022	11 m
5	41.40226	1.1 m
6	41.402264	0.11 m (11 cm)

For longitude, the same table holds at the equator. Moving toward the poles, each unit of longitude covers less ground, so east-west resolution gets finer than shown. See how long a degree of latitude and longitude is.

Resolution is not accuracy

A coordinate can be written with 10 decimals and still be wrong by 10 metres. The digits tell you how finely the number is expressed; the accuracy depends on where the position came from. A phone in open sky is often good to within a few metres, and worse near buildings or indoors. Read GPS accuracy vs precision for more on this difference.

Stating many more decimals than your source can support gives a false impression of exactness and can sometimes mislead people who read the data later.

Choosing how many to keep

• City or area, a few kilometres: 2 decimals is enough.
• Street or neighbourhood: 3 or 4 decimals.
• Building or doorway: 5 decimals.
• Surveying and engineering work: 6 or 7, and only with equipment that can really measure to that level.

For most delivery and checkout uses, five decimals is a practical rule, since it matches the accuracy that consumer devices can reasonably deliver.

How this relates to location codes

A grid-based code replaces long decimal strings with one short identifier for a small cell. UPCS codes represent a 3 m by 3 m cell, which sits between the fourth and fifth decimal place in terms of ground size. Why that size is chosen is explained in why a 3 metre grid cell is practical.