The fundamental diagram is a key component of traffic flow. It describes equilibrium traffic states and their propagation on a traffic network. The knowledge of its parameters is of paramount im- portance to understand traffic properties and its characteristics. It is also critical to calibrate the elements of dynamic traffic flow simulation models and reproduce traffic states on road networks. The paper is concerned with developing a method for estimating fundamental diagram parameters that combines loop data and probe data. Loop data are considered as boundary conditions of the problem. Travel times between (any points located between) the loop can be estimated based on the fundamentals of the kinematic wave the- ory. The optimal fundamental diagram parameters are computed so that the discrepancy between estimated travel times and actual travel times from probes is minimal.The method is validated on simulated error-free data. The results demonstrate the accuracy of themethod when applied on an error-free dataset. The method is then implemented using realisticdata, i.e. aggregated and noised beforehand. It demonstrates its robustness and the results are en-couraging for developing a algorithm that calibrates online and automatically fundamental diagramparameters.