Typical size distributions in regions of a protoplanetary disk model that are either turbulence-dominated (dark red lines) or drift- dominated (blue lines). Both regimes result in distinct power-law exponents of the distribution that we overplot as dashed lines. Assuming a power law as the overall shape of the distribution makes it possible to approximately describe it with only three parameters: The cutoff particle size a_max and the two densities Σ₀ (contained in the size interval [$a_{\min },\sqrt{a_{\max }{a}_{\min }}$) and Σ_ɪ (contained in the size interval [$\sqrt{a_{\max }{a}_{\min }},a_{\max }$]). This approximation is the basis of our new dust coagulation model.