 Determining the number of copies of a double stranded DNA template (be it genomic DNA, plasmid or an amplified fragment) is essential for many genetic quantification applications in research and diagnostic settings. When preparing standards for a standard curve, for example, knowing the number of copies you have in your DNA stock is essential to be able to work out a dilution series.

This can easily be achieved with a copy number calculator, all you need to know is the concentration of DNA in your sample in ng/µl and the length of your template in base pairs. The concentration of DNA in the sample is normally determined using a quantification tool based on fluorometry or spectrophotometry.

The following equation is used to determine the number of copies of DNA template (values in green are provided by the user). Calculations are made based on the assumption that the average molecular weight of a base pair (bp) is 650 Daltons.

Number of copies of DNA template per µl = (DNA concentration (ng/µl) x Avogadro's number) / (length of template (bp) x conversion factor to ng x average weight of a base pair (Da))

Number of copies = (DNA concentration (ng/µl) x [6.022 x 1023]) / (length of template (bp) x [1x109] x 650)

I have a stock sample of genomic DNA which has a concentration of 45 ng/µl and the genome size is 2,300,678 bp. How many copies of the genome are in 1 µl of this stock?

Number of copies = (45 x [6.022 x 1023]) / (2300678 x [1x109] x 650)
= 2.7099 x 1025 / 1.4954407 x 1018
= 18121079.6256 copies/µl
=1.81 x 107 copies/µl