How big is the opening in the seat? Sunny August 10, 2018 21:42 Updated Follow The opening in the Elongated Omigo is 11.5"L x 8"W. The Round Omigo is 10.75"L v 8"W. Download our Omigo Specification Sheet for more technical details. If you have any questions, please contact us. Related articles Will Omigo fit on my toilet? What maintenance is required? Can Omigo be used by children, elderly, and handicapped? When will I receive my order? What is the installation process?