How many months have 28 days?

All twelve months have 28 days.

While it is true that Feb has precisely 28 (or 29) days, the question in this post is usually intended as a trick riddle.

The answer to that riddle is "all 12 of them".

All months in both the Gregorian and Julian calendars have 28 or more days. The details are:

The Gregorian calendar has four months with a length of 30 days and seven months that are 31 days long. February is the only month that is 28 days long in common years and 29 days long in leap years.
The 12 Months of the Year
The Gregorian calendar and the Julian calendar both consist of the following twelve months:
January - 31 days
February - 28 days; 29 days in Leap Years
March - 31 days
April - 30 days
May - 31 days
June - 30 days
July - 31 days
August - 31 days
September - 30 days
October - 31 days
November - 30 days
December - 31 days

http://www.timeanddate.com/calendar/months/