Measuring fence hight for permit? Anybody know the regulations?

Hey guys/guyzettes etc. I'm in the process of building a rear yard fence on my property. Got some pickets to nail up recently and measured them they are 6 foot 1 inches. Even touching ground (wouldnt want to do that anyway) they would still technically be above 6 feet. Anybody know if there is some tolerance leeway or how exactly it's measured... seems weird the city would force me to cut 400 odd pickets.