A method of measuring the diameter of wide-aperture laser radiation for verification of the characteristics of optical beam-forming systems is developed. An experimental plant for precision measurement of beams with diameter up to 250 mm is fabricated. A technique for performing the measurements and processing the data is described. The structure and estimator of the measurement error, which amounts to less than 2%, is presented and ways of reducing the error down to a level less than 1% are proposed.