Production is hampered by sand and scale that impede flow and require intervention. Although coiled tubing jetting tools have been very successful in wellbore cleaning operations, the coiled tubing unit has certain limitations and constraints. The fluid pumping pressures of fluids at the wellhead are limited to the normal pressure of pump, whereas some sand types and scales require a very high shear force to break and disintegrate. The dimensions of the coiled tubing unit nozzle size are directly related to the diameter of the production tubing. The present work consists in designing the nozzle of coiled tubing jetting tool with different dimensional parameters and analysing the design of the nozzle for required high outlet pressure, flow rate and velocity at various inlet pressures. Numerical technique was used to analyse the flow of fluid through the nozzle. The different port diameters and cone angles between 0.09 and 0.125 inch and 15° and 45°, respectively, were simulated. The effects of these parameters on the outlet pressure, the mass flow at the outlet and the outlet velocities were predicted and analysed. Inner nozzle diameters smaller than 0.75 inch gave good results, and the 1 inch inner diameter gave lower performance. Therefore, the lower diameter nozzle provides better performance. Decreasing the number of ports from seven to five did not create a big difference in nozzle performance, as the seven ported nozzles provide slightly better performance. © 2019, The Author(s).