So far, scale-up theories on twin-screw extruders have not exactly shown the way toward proper scale-up. In the present work, by focusing on the specified scale-up to keep resin temperature unchanged, a new scale-up procedure has been proposed. It is shown that a new heat-removal-related parameter is necessary to describe, exactly, laboratory operation status. Scale-up criteria are delivered in an orthodox way, starting from extruder heat balance and also including a heat-removal parameter and a non-Newtonian index, which specify extruder conditions and polymer characteristics. The solution of this procedure can be easily obtained visually or numerically. Applying this procedure, a sensitivity analysis on;scale-up has been done considering the influence of the adiabatic index and the non-Newtonian index.