In this letter, I introduce Root Mean Squared Error (RMSE) based on the Fisher information matrix to evaluate the accuracy of distance-based location estimation. This qualitative index, which introduces the concept of the distribution of ranging measurement errors, allows a more precise evaluation of position estimation accuracy than the conventional Position Dilution Of Precision (PDOP). Visualizing PDOP and the proposed RMSE as a distribution over the evaluation space clarifies their respective characteristics. By computer simulations, I show usefulness of the propsoed index by comparing with Least-Squares estimation.