Scale proportioned S gauge engines and rolling stock are 1:64th the size of the real thing. 027 locomotives and rolling stock are smaller than 0 scale, which is 1:48th the size of the prototype; 027 equipment is no particular scale in most cases, but some of it is close in size to S gauge.
As an example, some of the earlier Marx rolling stock was 3:16th scale, or 1:64th S gauge proportioned. As a matter of fact, K- line used the old Marx tooling to make plastic 027 freight cars. K- line also used the same tooling with S gauge trucks to make S gauge freight cars by putting new trucks and couplers under the 027 bodies.
The initial answer to your question is 027 equipment is often wider and bigger than S gauge equipment, but not always.
In an upcoming article in OGR I will be talking about S gauge Marx freight cars that were marketed as O27 items.
This should be a start for you.
Hope it helps.
Ed Boyle
