To objectively analyze the gas tamponade area in patients with different concentrations of perfluoropropane (C3F8) after pars plana vitrectomy (PPV), retrospective analysis was performed in patients diagnosed with retinal detachment or macular hole and underwent PPV with C3F8 tamponade of two concentrations (14% and 20%). The ultra-widefield fundus (UWF) images at one and 10 days and four weeks postoperatively were corrected using stereographic projection to adjust peripheral distortion. The gas-fluid interface curvatures were delineated using UWF stereographic projection images, and the gas-fluid area ratio and estimated gas area were calculated at each concentration. Among 65 eyes, 30 were in the 14% group and 35 were in the 20% group. The gas-fluid area ratio was 0.71 in the 14% group and 0.83 in the 20% group at 10 days (p = 0.046) and 0.27 and 0.45, respectively, at four weeks postoperatively (p < 0.001). The estimated gas area was 52.56 and 60.82 mm2 at 10 days (p = 0.025) and 19.83 and 33.86 mm2 at four weeks (p < 0.001). The gas tamponade areas were objectively shown to be greater under the 20% concentration than the 14% concentration of C3F8 at 10 days and 4 weeks postoperatively using UWF stereographic projection images.