what is meant by "2i degree" how should we calculate it .

A 2i (or two-one) degree is the second best classification for a UK honours degree. It is also the minimum requirement for most PhD studentships. Students from outside the UK can check whether their qualification is equivalent to a UK 2(i) degree by contacting The National Academic Recognition Information Centre for the United Kingdom www.naric.org.uk. There may be a charge for this service.

if you have a total avearge between 60-70% your moduals, then you have a good chance of a 2.i