How tall is an O scale train? It varies. It can vary quite a bit. But I can give you some general guidelines. I can do the same for a related question, how long an O scale train is. Why the height of an O scale train variesThe height of an O scale train varies for two reasons, one more obvious than the other. The more obvious of the two reasons is because real trains can vary in height at least slightly. But the second reason is because not all of what we call O scale trains are actually true to scale. Many of them are undersized. But if you’re wanting to know the height so you can make sure your openings for tunnels or other passageways are big enough, that’s probably good news. It means you’re more likely to make the opening too big than too small, so the train will fit. In the worst case scenario, it just won’t look quite right. How tall a train is, and how to scale it down to O scaleA modern diesel locomotive is a little less than 16 feet tall. Calculating O scale dimensions from real-world dimensions is easy. Just divide the height in feet by four to get the height in inches. Sound too easy? O scale was supposed to be easy, that’s why it caught on. So the math says an O scale train engine should be around 4 inches tall since the real thing is around 16 feet tall. So if you want to be really careful, make your opening a little more than 4 inches tall. Four and a half or five inches ought to do it. Just be sure to compare my measurements with whatever O scale engines you happen to own. It’s highly unlikely yours will be taller than that. But you may find yours are smaller, especially if you’re into vintage trains like I am. I only own two engines that are close to 4 inches tall. The rest of mine are quite a bit shorter than that, because they’re actually undersize. Postwar Lionel engines often end up being closer to 3.5 inches in height, because they’re actually closer to 1:55 scale than 1:48 scale in many cases. But that’s one reason vintage Lionel trains go so well with holiday ceramic villages like Dept 56. Their scale varies too. How long is an O scale train? Every year starting in November, I get one or two people asking me how long an O scale train is, insisting on an easy answer. Well, unfortunately, there’s no simple answer for that. Here’s the simplest answer I can give. Each component of the train will be around 10 inches long. So if you have an engine and 3 cars, the whole train will be about 40 inches long. But again, since a lot of O scale trains are actually undersize, it could be less. Ten inches per car is a fairly safe estimate. Unfortunately the answer doesn’t get any simpler than that, since I don’t know how many cars you have, and not all cars are even the same length.