Things You'll Need
Instructions
Measure the area or table where the train set is going to go.
Head to the hobby shop. Bring the tape measure.
Measure out a few pieces of track in each scale. The most common scales are O, S, HO and TT, listed from largest to smallest.
Do the math if you don't have a tape measure. Sizes are as follows: O track is 1 1/4 inches wide. S track is 7/8 inch wide. HO track is 0.65 inch wide. TT track is 0.47, or about 1/2, inch wide.
Decide how much detail you'd like to have on your trains if room is not an issue. Detail is easier to see and reproduce on larger trains.
Consider how extensive you intend your layout to be. HO scale is the most common and has the widest variety of accessories available.
See whether the trains and accessories you like are available in every scale or only some scales, and choose accordingly.