This paper proposes weighted dilution of precision (WDOP) as an indicator of the accuracy of position and attitude in vision-based navigation. WDOP accurately represents the tendencies of navigational errors. It is obtained by weighted least squares. The weight is determined by the deployment of feature points and the geometrical distortion of the vision sensor. The performance of WDOP was verified by simulation. The values of the dilution of precision (DOP) and WDOP were computed and analyzed by comparison with the navigational errors. Additionally, a correlation test was used to determine how well they reflect the trends of the navigational errors. Simulation results showed that WDOP was strongly correlated with navigational errors, which makes it a parameter that can be used to determine the quality of a vision-based navigation system. The proposed WDOP can be used as a practical indicator of navigation performance.