I have a five shot S&W 642 and the gun will fit in a pocket because of its light weight (15 ounces empty) and smooth contours. But it is not easy to shoot well and is really a "last ditch" gun to use at close range.
I also have a Colt Detective Special that is all steel and heavier (21 ounces empty), holds 6 rounds, and is much easier to shoot accurately at intermediate range than the 642. The Colt conceals very easily in a belt scabbard type of holster and is so small you aren't really aware of it on your belt, as you would be with a larger gun. I much prefer the Colt for shooting, and feel better armed with it on my belt, than with the 642 in my pocket.