Objective To determine the 90% minimum effective volume (MEV90) of ropivacaine for ultrasound‑guided pericapsular nerve group (PENG) block to anesthetize the lateral femoral cutaneous nerve during hip surgery with the up‑and‑down biased coin design (BCD). Methods Patients with American Society of Anesthesiologists (ASA) grade Ⅱ or Ⅲ who underwent hip surgery in Hongqi Hospital Affiliated to Mudanjiang Medical University from July 2022 to March 2023 were selected. They were subject to ultrasound‑guided PENG block 30 min before general anesthesia induction. Then, the up‑and‑down BCD method was performed. The dose of 0.375% ropivacaine for the initial patient was 20 ml. The dose of ropivacaine for the next patient would depend on the block results of the previous patient, where the adjacent dose gradient was set to 2 ml. If the block failed, the dose of the next patient would increase by 2 ml. If the block succeeded, the dose of the next patient would be reduced by 2 ml at probability of 11%, and would remain the same at a probability of 89%. The test would come to the end when there were 45 successful cases. The dose of ropivacaine for each patient was recorded. MEV90 was calculated through isotonic regression and the 95% confidence interval (CI) of the result was calculated through the bootstrap algorithm. Their age, sex, body mass index (BMI) and operation time were recorded. The time of PENG block operation, the time to successful onset of PENG block, the total intraoperative dosage of remifentanil and sufentanil, the time of first compression of patient‑controlled intravenous analgesia (PCIA) pump, rescue analgesia within 48 h after operation, the incidence of quadriceps movement block within 48 h after operation, and the incidence of other adverse reactions during the perioperative period were recorded. Results There were 53 patients, including 23 men and 30 women, where 29 patients were at ASA grade Ⅱ and 24 at ASA grade Ⅲ. The age was (65±13) years, BMI was (21.7±1.3) kg/m2 and the operation time was (2.9±0.9) h. The MEV90 of PENG block to lateral femoral cutaneous nerve was 27.09 ml, 95%CI (25.93, 29.79) ml. The time of PENG block operation was (3.1±0.7) min. The time to successful onset of PENG block was (18±5) min. The intraoperative dosage was (18.7±2.0) μg for sufentanil and (0.26±0.08) mg for remifentanil. The time of first compression of PICA after operation was (11±5) h. The dosage of ketorolac tromethamine for rescue analgesia within 48 h after operation was (22±21) mg. Motor block of the quadriceps femoris occurred in 31% of patients 2 h after operation, and there was no motor block within 48 h after operation. There were six cases of transient hypotension, five cases of postoperative nausea and vomiting and one case of subcutaneous hematoma. Conclusions Using 0.375% ropivacaine for ultrasound‑guided PENG block can block the lateral femoral cutaneous nerve with a MEV90 of 27.09 ml, which can improve the anterolateral thigh analgesia.