Including January and March, it's 13 weeks. In regular years it is 12 weeks and 6 days, and in leap years it is exactly 13 weeks.
If referring to the period from the beginning of January to the beginning of March or from the end of January to the end of March (or middle to middle, etc.), it is eight weeks and three days in regular years and eight weeks and four days in leap years.
12 weeks 5 days
21 weeks and 5 days!
A little over 43 weeks between March 4 2010 and January 5 2011.
A little over 12 weeks from 1st January 2011 until 31st March 2011.
11 weeks and 5 days.
As today is January 27, there are 61 days or 8 weeks and 5 days until March 29.
10 weeks, 2 days
41 weeks and 3 days.
45 weeks and 1 day.
For the 6 months of January, February, March, April, May and June, there are 25 weeks and 6 days in a normal year and 26 weeks in a leap year.
Including the dates given there are 90 days or 12 weeks and 6 days.
There are 4 weeks in January 2011