Economy travellers on united airlines carry on size are permitted to bring one carry-on bag, as long as it doesn't exceed 9 inches by 14 inches by 22 inches (22 cm by 35 cm by 56 cm). The overhead bin should accommodate this bag. In addition, passengers are permitted to bring one personal item that fits under the seat, such as a laptop bag or pocketbook. Passengers in premium cabins may be eligible for additional or differing allowances. For the most up-to-date and accurate information on carry-on size restrictions, it is advised to visit United Airlines' official website or get in touch with the airline as regulations are subject to change.