I would say it’s a 6” barrel. I believe the gun is slightly angled in the picture giving the barrel a somewhat shorter appearance. Also the ejector housing looks to be about half the length of the visible barrel; on a 5” barrel the ejector housing is well over half the length of the visible barrel.
Did five inch 27-2s come with Patridge front sights? I have several and all have ramp front sights. My six and 6.5 inch 27s (and 8 3/8) have Patridge. I guess put me in the six inch camp for now.
Here is a better pic of the barrel and front sight. Seller insists its a 5" but as was posted here the front sight seems wrong and also the ramped section below the sight on a 5" appears to go all the way back above the stamped "Smith and Wesson" on the barrel. This one does not.
Just to add to what has been said above; a 3 1/2” barrel goes just past the shroud and it looks to me that there are another 2 1/2” past that. It is a 6”.
Very likely the seller is making the common mistake of measuring from the frame rather than the face of the cylinder.
I have no doubt that that is a 6".