Concentration profiles on the different sites of tungsten screw dislocation are calculated as a function of the nominal carbon atom concentration, temperature and dislocation density. Rigid lattice Monte Carlo simulations and associated mean-field modelling are performed based on interaction energies from ab initio calculations. We show that the repulsive interactions induce ordering phenomena that drastically change the concentration in the core of the dislocation and leads to ordered structures among the octahedral sites. We detail the domains of short-range ordering (SRO) and long-range ordering (LRO).