Outer Dimension: 30-1/8" x 18-5/8", Dome Dimension: 27" x 15-3/4" x 5-1/2" Made of durable, impact resistant polycarbonate Industry leading quality skylight - Thicker and stronger than the original OEM skylight Take the dimensions of your skylight opening on your RV and compare them with this skylight to ensure a proper fit for your unit Use ICON Skylight Sealant for install