Dispersion engineering and measurement are significant for nonlinear photonic applications using whispering gallery mode microresonators. Specifically, the Kerr microresonator frequency comb as an important example has attracted a great amount of interest in research fields due to the potential capability of full integration on a chip. A simple and cost-efficient way for dispersion measurements is thereby in high demand for designing such a microcomb device. Here, we report a dispersion measurement approach using a fiber ring etalon reference. The free spectral range of the etalon is first measured through sideband modulation, and the dispersion of the etalon is inferred by binary function fitting during the dispersion measurement. This method is demonstrated on two MgF2 disk resonators. Experimental results show good agreement with numerical simulations using the finite element method. Dispersion engineering on such resonators is also numerically investigated.