A frequent question, especially for those who are just discovering or rediscovering vintage Lionel and Marx trains is what sizes of track are (or were) available, and how many pieces come to a circle.
Unlike other scales, Lionel marketed its track by diameter, not radius. As you undoubtedly remember from geometry class, radius is the distance from the center of the circle to the edge, while diameter is the distance from edge to edge. So a circle of O27 track is approximately 27 inches wide. O27 track stands about 7/16 of an inch tall, while higher end O gauge (also sometimes called O31) track stands about a quarter inch taller, at about 11/16 of an inch tall.
While we’re on the topic of track, here are some tips for connecting track if your new track isn’t going together as easily as it could.
Here are the available sizes, in ascending order.