What kind of tomatoes- determinate or indeterminate? For determinate you'll probably be okay. For indeterminate you'll need a lot more, the vines can get 6-8'.
It looks like I have all indeterminate varieties with the exception of Celebrity. The others are super sweet 100, yellow pear, san marzano and the burpee big boy. Does that mean that even if the plant is expected to grow to 36'' to 40'' I need a large cage because the vines will be longer than that?
I've heard there's compact varieties, but the ones I've gotten always just keep growing until the end of the season. Because there's no *determined* end point. I either stake or do a Florida weave. I like the Florida weave method a lot, but you have to keep up with it.
I've also noticed plant size on tags usually just means the size they got when the grower decided they were done. Not just tomatoes, but perennials too. Sometimes the size will show the three year growth, but it's a plant that really takes off in its 5th or 10th year. I see the marked sizes as suggestions.