This paper presents a method for joint estimation of fiber and fines mass fractions (i.e. pulp consistency) in paper pulp suspension. The technique is based on a combination of optical and ultrasonic measurements. The link between measured quantities and the mass fractions is established through Partial Least-Squares Regression (PLSR). The method is evaluated with experiments on unbleached softwood pulp for a total mass fraction of fibers and fines ranging from 0.6% to 0.54%. The results show that we are able to accurately predict both the fiber and fines mass fractions using the proposed technique. We also show that the performance is increased by combining the two techniques compared to using them by themselves.