I think it is not possible to make a non integer cell. Can u please refer me a paper in which such type of calculations are mentioned ? 

You can do that with structeditor program written by Robetrt laskowski. This script was included in WIEN2K package. 

In general, one have to use integer number to increase the multiplicity. This is the case when dealing with alloys for example. 

I am sorry to say that I have still confusion on it. Could any  one please tell me clearly . I have seen so many papers, in which they formed fractional supercell. I am giving the citation of one paper here:

Phys.Chem.Chem.Phys.,

2015, 17, 26979

Hi Priyanka Garg,

I would also like to know how to make an incommensurate supercell. Could you please help me out if you have solved this issue?

Following links are relevant to this question:

https://mattermodeling.stackexchange.com/questions/6486/help-understanding-square-root-notation-of-supercell

https://mattermodeling.stackexchange.com/questions/11953/how-to-make-pd111-supercell-%e2%88%9a3%c3%97%e2%88%9a3r30-via-vesta