Outside diameter of Lionel tubular o-42 radius track?

O-42 is 20.17" center rail radius / 40.34 center rail diameter, so should be about 42.89" - 43.06" diameter nominally over the ties. Call it 43.

Thanks Rob. It seemed like I was bending it too tight when I tried to get it 42". Wonder where they came up with 0-42? 43" still works for me though.

O-42 is most likely 42" diameter, measured center-to-center of the outside rails.

I don't have any O-42 track, but I have some Menard's O-36 tubular track that just so happens to measure 36" diameter, once again center-to-center of the outside rails.

That makes sense Paul. Just thought they would stay consistent and go with the outside of the tie like O-31 or the center like 0-72. But hey, this is o-gauge.

I don't have the measurements to the outside edge of the track, but here are the measurements center-rail to center-rail.  Take a measurement from center-rail to edge of track and add that.  I've read that for O-27 and O-31 the measurements were to the outside edge.  For O-72 it was center-rail to center-rail.  Don't know about O-42 or O-54, although one post mentioned they were from outside-rail to outside-rail.  Again, these measurements are center-rail to center-rail and from previous forum topics.

O-27     24.75"

O-31     28.3"

O-42     41" ( a little different than Rob's measurement)

O-54     51.7"

O-72     71.75"

Thanks for everyone's feedback. I took that 43" number and built the layout 66"x 9' and it worked out perfectly. Still have to finish the control panel but it turned out to be a nice Christmas layout.

@Mixed Freight posted:

O-42 is most likely 42" diameter, measured center-to-center of the outside rails.

It's 40.34".

I get an inch and 1/8th from the center to the outside of the cross tie. that's 2 & 1/4" added to the diameter of 042. Total of 43 &1/4"