Large telescopes require a very precise calibration in order to maximize its scientific output. Current catalogues of standard stars are generally too bright for 10m telescopes. For GTC we are planning to produce a catalogue with calibration stars which are suitable for this telescope. In this paper we describe the first steps of the GTC calibration plan. This will require spectrophotometric calibration standards between 0.35 and 27 microns applicable to the GTC science instruments: OSIRIS (Optical System for Imaging low Resolution Integrated Spectroscopy), ELMER and EMIR (Espectrografo Multiobjeto Infrarrojo) as well as the Acquisition and Guiding boxes.