How thick is the earths crust on an average?
Thank you

It varies around the planet. Here's a good explanation:
http://quake.usgs.gov/research/struc...stalStructure/

Rickj is right--thickness varies.

mean thickness = 24 mi (40 km), standard deviation is 5.4 mi (9 km).

thinnest = approx 9 mi (15 km)

thickest = 47 mi (75 km)