The Wikipedia page Decimal Degrees has a table on Degree Precision vs. Length. Also the accuracy of your coordinates depends on the instrument used to collect the coordinates - A-GPS used in cell phones, DGPS etc.
decimal
places degrees distance
------- ------- --------
0 1 111 km
1 0.1 11.1 km
2 0.01 1.11 km
3 0.001 111 m
4 0.0001 11.1 m
5 0.00001 1.11 m
6 0.000001 11.1 cm
7 0.0000001 1.11 cm
8 0.00000001 1.11 mm
If we were to extend this chart all the way to 13 decimal places:
decimal
places degrees distance
------- ------- --------
9 0.000000001 111 μm
10 0.0000000001 11.1 μm
11 0.00000000001 1.11 μm
12 0.000000000001 111 nm
13 0.0000000000001 11.1 nm
