What is the inner circumference of the tube? October 23, 2024 15:23 The inner diameter is approximately 20" and designed to fit one person comfortably. Related articles Is there a non-skier viewing area for ski school? Do you offer an early bird "First-Tracks" Program? Is there a height or age requirement or limit to your activities? What are the tubing discounts? How fast do the tubes go down the hill?