Although excessive force on organs is known to cause injury, learning how to safely apply force during surgery is one of the most difficult skills for young doctors to master. Based on their experience, expert surgeons have their own safety thresholds and operate within these thresholds. In this study, we investigated these “safety thresholds.” The experiment was conducted after obtaining approval of the Ethics Committee of the Animal Experiment Facility (IVT24–50). We performed experiments in the same setting as laparoscopic surgery using a laboratory pig. Two expert surgeons who are responsible for teaching and supervising surgery at their respective institutions compressed the pig’s kidney for a few seconds at the appropriate safety threshold strength used in actual surgery. The force was measured using surgical forceps equipped with a three-axis force sensor at the tip. The measured force was graphed and the mean force over a 1-s interval following the first peak was calculated (1sMean). The median of 1sMean in 337 sessions was 0.79 N (interquartile range: 0.62–1.04 N). The logarithmic transformation of 1sMean became the normal distribution. The exponentially transformed mean, + 1SD and + 2SD were 0.80 N, 1.19 N and 1.76 N, respectively. In minimally invasive kidney surgery, expert surgeons are taught to target a force of about 0.80 N, with a safety margin of 1.19 N and a safety limit threshold of 1.76 N. The results of this study can be used as basis for future studies on the forces applied to the organs.