28 (twenty-eight) is the natural number following 27 and preceding 29.
In mathematics
thumb|The number 28 depicted as 28 balls arranged in a triangular pattern with the number of layers of 7
thumb|28 as the sum of four nonzero squares.
28 is a composite number, a happy number, and a perfect number.
28 also appears in the Padovan sequence.
In science
- The fourth magic number in physics.