The length of DNA in a human cell is about

The distance between two consecutive base pairs = 0.34nm or 0.34 x 10^-9 m
If the length of DNA double helix in a typical mammalian cell = The total number of bp x Distance between two consecutive bp 
                                                                                                 = 6.6x 10⁹ bp x 0.34 x 10^-9 m/bp = 2.2 m.
The length of DNA in a human cell is about 2.2 m.