Pressure-less spark plasma sintering (SPS) is a new approach during which rapid densification of ceramic nanopowder green bodies is accompanied by rapid grain growth. Although the origin of this phenomenon has not yet been fully understood significant, difference in grain growth between pressure-less and pressure-assisted SPS was expected. In this work 3Y-TZP nanopowder with average particle size of 12 nm was consolidated using two-step approach: (1) at an intermediate temperature (600 degrees C to 1000 degrees C) SPS warm pressing followed by (2) high temperature (1400 degrees C to 1600 degrees C) pressure-less SPS. The standard one step pressure-assisted SPS experiments were quoted as references. Rapid grain growth was observed during both pressure-less and standard SPS. The samples prepared by both approaches at the same sintering temperature (1400 degrees C1600 degrees C) achieved identical grain size and grain size distribution, if large pores were eliminated in early stage by SPS warm pressing. The electric current, electromagnetic field, and mechanical pressure is proven to have a negligible direct influence on grain growth in 3Y-TZP ceramics at temperatures above 1000 degrees C under standard SPS conditions.