How much time for St. Peter's Basilica?

Just a data point ... on Friday May 29 my grandson and I arrived in St. Peters Square at 8:15 am and stood in the security line for a little over half an hour to enter the basilica. The end of the line when we joined it was halfway around the circumference of the piazza. By the time we left the basilica at about 10 am the line was all the way around the piazza.

But it was worth it. :)

Time needed to see the 'main area'? For me, one hour minimum and up to three hours, depending on your level of interest and curiosity.

Getting there early is a good idea. Access to the dome is not possible til 8am so initially look at the Basilica. We took about 2 hours to ascend the dome and return to ground level last time we were there. We went at a very leisurely pace with a long stop at the top to enjoy the view and a coffee stop and sit in the sun on the roof top. You could go quicker and your pace will be determined by your fitness given the number of stairs.

Go as early as you can, and you'll see shorter lines.
You should be able to go through there in a couple of hours--total.
And if you're also going through the Vatican Museum, you should consider buying tickets with reservations prior to going..

So how does 7am Basilica, 8am Dome and done by 9:30am, then 10am Vatican Museum tour sounds? Is that do able? I'll reserve Vatican Museum tickets in advance.

We were at the Vatican in July and did the Pristine Sistine tour with Walks of Italy. We had a lovely time in the Sistine Chapel and a good overview of the museum before it got insanely crowded. By the time we got to the Basilica (at about 10:30, I think??), it was an absolute mob scene. There were massive tour groups - thirty people wide and thirty deep - massed in front of everything. We could not get close enough to the Pieta to really even see it. The security officers were doing the best they could to manage people but it was impossible. Our tour guide did his absolute best to get us around the church but the crowds were truly immense.

If I had it to do over again, I would break the Vatican into two days. I would arrive as early as possible to tour the church. If the Basillica opens at 7, I would arrive and get in line well before that. That should give you an opportunity to see the splendor of the church without so much of a crush and climb the dome (which we did on our last trip but not on this one). Then I would arrange the earliest possible Vatican museum entrance for another day, head straight back to the Sistine Chapel, and then circle back and do the rest of the museum. By 10am the crowds in the museum were stiffling.

The Vatican is truly spectacular but because of that, it is crushed by tourists. We actually tried to go back very late in the evening just so we could see the Pieta - the lines at 6:30pm were still astounding and we could not get in.