Dimensions of a circle O31 track

That should work . JohnA 

A regular O-31 "O Gauge" track circle is nominally 31" in diameter including the ties, and has a 14.14" center rail radius(28.28" diameter).  A circle of O-36 FasTrack is 40" in diameter including the roadbed, with a 18" center rail radius.

Also, you may want to utilize CO-1 track clips, which slide between the ties and lock them together.|

031 is approximately 31 inches diameter.

Merlin - Assuming you're talking about 'tubular' track sections coming apart, have you considered getting some Lionel 'Track Clips' which hold each section to the next?  They have them for both 027 and 031 track and they're inexpensive.

Just a thought.

Id add a couple of inches to the OD on some

A sprial rope rug usually has good support and thickness, stable near edges and doesn't shed synthetic thread/fuzz into gears, etx. (they make oval and square spiral too.) It may be of plain rope or (softer) cotton rope. 

A softer rug under that is a bonus, but a plain soft rug is unstable. If the track sits too hard , even the rope can scratch. Keep it's edges clean of scratching dust and sands that creep under.

A string of lights around the outside dia.  31×π=97.3893" long.

I did buy the black clips for the lionel fasttrack but they were popping off the longer the train ran. I always had carpet until I switched to hard wood last year. I dont understand some of the dimensions given here. I am just asking if I run my polar Express using fasttrack O31 would a 4 feet round rug be enough to have the O31 track on it?

As ADCX Rob said its about 31" in diameter. Your 4 foot rug would easliy accommodate that.

Additionally, throw a tape on the actual "Four foot diameter rug" before you buy it.  Area rug sizes are soft numbers.  Frequently slightly undersized.

Thanks everyone for your replies I really appreciate it. This is the carpet I bought for the Christmas tree and the fast track. https://www.amazon.com/Safavie..._pdt_img_top?ie=UTF8

@Scotie posted:

As ADCX Rob said its about 31" in diameter. Your 4 foot rug would easliy accommodate that.

@Merlin posted:

I did buy the black clips for the lionel fasttrack but they were popping off the longer the train ran. I always had carpet until I switched to hard wood last year. I dont understand some of the dimensions given here. I am just asking if I run my polar Express using fasttrack O31 would a 4 feet round rug be enough to have the O31 track on it?

Well, now that you have clarified that you have FasTrack 31, not O-31, your circle of O-31 FasTrack is 35" in diameter including the roadbed, with a 15.5" center rail radius, giving you about 6.5" clearance on all sides to the edge of the carpet. The CO-1 clips will not work, the smallest binder clips you can get snapped on will keep the sections together.

Like Rob alluded to, get a small package (8-12) of black binder clips (I use 3/4" wide) like the ones used to hold sheets of paper together. Assemble your circle of Fastrack and flip over. Attach a binder clip to the underside of the trackage where each track section meets the next one and fold down the silver metal tabs making sure they do not touch any of the Fastrack tabs (you can remove the silver metal tabs once the binder clips are in place if you want). The binder clips will hold the track together and prevent any track sections from coming apart. They also help with insuring good connectivity between track sections.