Characteristics of batch rotor–stator mixer performance are elucidated by shaft torque and angle resolved 2D PIV measurements obtained in a full-scale, custom build, bottom-mounted, rotor–stator mixer unit operating in the turbulent regime with water as working fluid. Measurements have been acquired at various rotor speeds corresponding to impeller based Reynolds numbers between 2.0 × 105 and 8.5 × 105. The use of a transparent Plexiglas stator facilitated PIV measurements inside and outside the stator as well as into the stator slots themselves. The governing mechanisms controlling the complex flow structures, flow rates, power dissipation, velocity fields, strain rate fields and turbulence intensity fields are explained, highlighting the influence on rotor–stator mixer performance. The results indicate that scale-up of mixing processes that depend on macro-scale phenomena should be based on constant rotor tip speed.