How big is the opening in the seat? Toshi 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 Do the nozzles ever get in the way? Can Omigo be used by children, elderly, and handicapped? 90-Day Risk-Free Trial What maintenance is required? Where is Omigo serviced for repairs?