Abstract: The aim of this study was to determine the particle size, temperature, and amount of released fat for safe periorbital fat grafts. From 28 patients, fat was suctioned from the abdomen (large particles [LPs]) and from the inner thigh (small particles [SPs]) using a 2.1-mm harvesting cannula with a diameter 3.2 × 1.4-mm hole and a 1-mm hole, respectively. The 10-mL syringes full of fat were then put into a centrifuge for 3 minutes (LP) and 1 minute (SP) at 3000 revolutions/min. Fat was then transferred to a 1-mL syringe with Luer-Lock adapters and a blunt cannula of 0.9-mm diameter. The force needed to push the fat out of the cannula was measured with a force gauge. The force was measured within the different groups according to particle size of the fat, temperature of the fat, and released amount of fat. The force needed to push the SP fat out of the cannula into the air with minimal amount (MA) (0.01–0.02 mL) injected at room temperature (25°C) (1.75 ± 0.82 N) was significantly greater (P = 0.000 [t test]) than at body temperature (BT, 33°C) (1.27 ± 0.38 N). At BT, the force needed to push the SP fat into subcutaneous pig tissue (2.30 ± 1.46 N) was significantly lesser (P = 0.000 [t test]) than LP fat (6.54 ± 2.39 N). At BT, the force needed to push the MA of SP fat into pig subcutaneous tissue (1.38 ± 0.26 N) was significantly lesser (P = 0.000 [t test]) than the force needed to push the usual amount (0.03–0.04 mL) of SP fat (3.83 ± 1.78 N). The force needed to push the fat into human lower eyelids at room temperature (4.06 ± 2.26 N) was significantly greater (P = 0.000 [t test]) than at BT (2.11 ± 0.96 N). At BT, the force needed to inject an MA of SP fat into human lower eyelids (1.55 ± 0.83 N) was significantly lesser (P = 0.000 [t test]) than the force needed to inject a usual amount of fat (2.78 ± 1.03 N). We suggest injections of the SP (1-mm hole diameter harvesting cannula) fat with MAs (0.01–0.02 mL) by means of fragmented incremental injections stored at BT (33°C) to reduce the injection pressure.