We compute an explicit formula for the integrated density of states of the periodic Airy-Schrödinger operator on the real line. For this purpose, we study precisely the spectrum of the restriction of the periodic Airy-Schrödinger operator to a finite number of periods. We prove that all the eigenvalues of this restriction are in the spectral bands of the periodic Airy-Schrödinger operator and none of them are in its spectral gaps. We count exactly the number of eigenvalues in each of the spectral bands, this number being equal to the number of periods to which the periodic operator is restricted, plus one. Note that our results depends on a semiclassical parameter but are not stated in the semiclassical limit. They are valid for values of the semiclassical larger than explicit constants.