Picomoles of dsDNA to Micrograms and Nanograms
How long is your DNA (in base pairs)?  
You have µg of DNA 

pmol DNA x  660pg x µg  x N = µg DNA
pmol 106pg

or

How many pmol of DNA do you have?
You have ng of DNA 
pmol DNA x  660pg x ng  x N = ng DNA
pmol 103pg

N is the number of nucleotides and 660pg/pmol
is the average molecular weight of a nucleotide pair.

Based on BioMath programs created and copyrighted by Promega Corporation.