I'll try and explain it in easier terms:
- The world is about 40,000 kilometers (25,000 miles) around.
- A latitude/longitude value breaks that distance up into 360 degrees, starting at -180 and ending at 180.
This means that one degree is 40,000 km (or 25,000 miles) divided by 360. Lets do the math for both of those:
- 40,000 / 360 = 111
- 25,000 / 360 = 69
So, one degree is 111 kilometers, or 69 miles.
For fractions of a degree, you divide it by 10 for each decimal place, as @ChethanS's chart nicely demonstrates (in km):
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 0.111 m
7 0.0000001 1.11 cm
8 0.00000001 1.11 mm