Day trip from Rome to Pompeii...too much for one day? How about switching trains in Naples? Does that work OK?
Lots of folks do it, although it is a bit much in a day. That said, doing it by train is definitely preferable to one of the bus tours that eat up too many hours on the road, IMHO. Here are some detailed instructions from the "Man in Seat 61" website.
https://www.seat61.com/places-of-interest/day-trip-to-pompeii.htm
One mention: the seat61 site includes some info on a Sunday train to Pompei that I've not checked for operation in summer of 2025, if it's even posted yet.
You can find more opinions using the Search box top left, usually in blue. Do you understand that the train boarded in Naples is not sold or ticketed by Trenitalia, and is more like a commuter train or surface-subway? It's right downstairs, by escalator and short walk.
Edit: There have been posts here saying that the Circumvesuviana is installing credit card Tap & Go turnstiles, but I find this hard to believe. It's like hearing that McDonalds is installing fingerbowls and napkin rings!
It strikes me as significant that the food recommendation below suggests that the poster did not learn while in Pompeii that there is an air-conditioned, glorified cafeteria restaurant inside Pompeii. That's important to some visitors because you cannot exit and re-enter Pompeii on a same-day ticket. Heat and sun are a huge factor in treeless Pompeii from May to September.
This is a topic that comes up frequently. Tim has given you a link to one of the conversations. I'd just like to recommend looking at Ostia Antica. It is about a 1/2 hour on public transportation from Rome. Easy. Beautiful place. Nice museum and cafe, lots of shade, many like it as an alternative to the grueling day trip from Rome to Pompeii.
You don't say if it's just you or it's a group? I did this on my own 2 years ago and it was not hard. I left at 9:00 a.m. and I was back in Rome around by 5:00 p.m.
Book a high speed rail ticket from Rome to napoli. Once in Napoli, you go downstairs to buy your ticket on the circumvesuviana train. You can't buy these in advance. Also read the directions on the Rick Steves book so you know where to go in the Naples train station.
The circumvesuviana train is more like a tram/trolley. You may or may not get a seat.
I prearranged a tour guide to meet me at the entrance. I booked it through Mondo guides - rick Steves book has the info. It will be a small group tour. I think 6 to 8 people maximum. Tour was from 11:00 a.m. to 1:00 p.m. there are cafes with sandwiches near the circumvesuviana station.
The only snag was I missed the circumvesuviana train back to Naples that I had planned, so I missed my pre-booked train back to Rome and had to buy another ticket. So I would recommend buying a flexible ticket for your return. Other than that it was easy.
With the fast trains, it is much more feasible than years ago.
Myself, I would plan to leave Rome early, so you could be at Pompeii near opening time. Guide/No Guide is up to you, there are plenty of resources for self-guided tours.
I would plan on spending about 3 hours at the sight. Many will say you need days, but for the vast majority of people 3 hours, plus or minus an hour works well, allowing you to see most of the important sights, without going into ruin overload or heat exhaustion if in the Summer.
That would leave enough time to stop for pizza in Naples and maybe a visit to the Archeological Museum.