I know this might sound dumb, however I am new at this Train business, so I have a question to ask. How do I know what size my trains are?
Assuming you are asking “What scale are my trains”. Look on the box[s] If you still have them. The scale (N,HO,O and others) ought to be marked upon the box. If you don’t have the box[s] anymore, look here:
http://www.nmra.org/standards/sandrp/pdf/S-1.2%202009.07.pdf
Measure you trains with a ruler and you will be able to match them up with a scale in the standard.
Alternately, if you are asking “How long should my train be?” most of us run as long a train as will fit on our tracks. Few to none of us have a layout big enough to fit the 100 car freight trains that the prototype railroads run.
For a 40’ boxcar, roughly speaking:
Z 2.5 inches long
N 3 inches long
HO 5.5 inches
S 7.5 inches
O 10 inches
G 15" +
Enjoy
Paul
Post a photo of one of the items with a ruler visible alongside the item, whether showing cm or inches. We’ll tell you in a jiffy.