Abstract The distinction between pressure in a liquid and in a gas is often treated in a cursory way, or not treated at all, even in university level textbooks. Most texts fail to point out the relation between pressure and density in a gas as compared to pressure in a—virtually incompressible—liquid. In many instances this also results in a dismissive treatment of atmospheric pressure. In this paper we suggest that in the physics curriculum of university and secondary school students, kinetic theory of gases be treated before fluid mechanics and thermodynamics. In this way, the definitions of pressure P and absolute temperature T in a gas can be derived consistently, with the remarkable advantage that the links between the macroscopic parameters P and T and the velocity of molecules—a microscopic parameter—are made clear at an early stage, as well as the relation between P and density ρ.