To optimize measurement procedures in laboratories, in terms of the balance between economics and risk, determination of the optimal calibration interval for measuring equipment has significant importance. This paper will show an approximate, but effective method for determination of initial calibration interval, regarding “ILAC” guidelines and original recommendations based on authors’ experience. The presented applied method is adapted for the equipment used in a laboratory for building materials and structural testing, and the results of its application are shown on the examples of several different instruments. Impact factors on calibration intervals are analyzed, and the basic recommendations for revision of the initial calibration intervals are given.