Calculating number of days in a month selected from a drop down menu

I have a drop down menu that allows me to select the current month. Is there a way to have excel calculate the number of days in the month based on the month I select? and is it possible to use the number of days in a forumal within the same document? For example: I would select January and on my form. I have a cell titled "Allotted units per payroll" (based on total number of days in the month multiplied by units allotted each day) so I need to take the units allotted for the month divided by the total number of days in the month and then multiple that number by days in each payroll (which will vary between 15 and 16 days based on days in the month) or is there an easier way to get what I want.

thank you
Anthony

Days in Month dropdown.xlsxI would use a vlookup from the result of the drop down to a chart that lists each month and the number of days. See attached.

Assumed your month formatted text "January" on A1:

=DAY(DATE(YEAR(MONTH(DATEVALUE(A1&" 1")));MONTH(MONTH(DATEVALUE(A1&" 1")))+1;1)-1)

thank you, works just fine.