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The fields in the core, the far-field radiation pattern, and the transmission through an offset splice for single-mode fibers all are well approximated by Gaussian functions. However, the method used to fit the Gaussian function to measured data influences the resulting width of the Gaussian, which is called the mode field radius. Of the fitting methods studied, only maximization of the launch efficiency integral gives values of mode field radii which are consistent between near-field and far-field measurement methods. The transverse offset measurement method is consistent with these two if an unweighted truncated fit is used. Also. two published analytical formulas for the mode field radius are studied, and only one of the two gives accurate values. A third analytical formula, which is simpler and more accurate over a smaller range of wavelengths, is presented.