Do you mean pUC18 and not pCU18? 

We commonly use pUC18 and pUC19. I have never used "pCU 18"

soory its pUC 18..  can we calculate it?? is there any formula for that??

Hi Milind,

You have 3.45*109 copies, if the length of your pUC18 is 2686bp.

This can be calculated using Avogadro number ( number of constituent molecules/atoms per mole of a given substance)

The formula is:

number of molecules = ( amount of DNA * 6.022x1023) / (Mol.wt of your dsDNA)

      - where 6.022x1023 is the Avogadro number.

       - the mol.wt of pUC18  = 650g (one mole of a bp)  * 2686bp (length of your DNA)

There's even an online calculator that does this for you, take a look at it, more so to understand the formula!   http://cels.uri.edu/gsc/cndna.html

hope this helps,Cheers