Methods may include estimating the weight fractions of kerogen and inorganic mineral components of at least an interval of a subsurface formation; determining the grain density of kerogen and inorganic mineral components, wherein at least the grain density of kerogen is determined by one or more infrared measurements; and calculating the formation matrix density of at least an interval of the subsurface formation from the estimated weight fractions and the determined grain density. In another aspect, methods may include estimating the weight fractions of kerogen and inorganic mineral components of at least an interval of a subsurface formation; determining the grain density of kerogen and inorganic mineral components, wherein at least the grain density of kerogen is determined by one or more infrared measurements; and calculating the formation matrix density of at least an interval of the subsurface formation from the estimated weight fractions and the determined grain density; calculating the bulk density for at least an interval of the subsurface formation; and determining the total porosity of at least an interval of the subsurface formation as a function of depth by combining the calculated formation matrix density and the calculated bulk density.