Leave enough time to follow the museum route without rushing. Reaching the chapel is not a short standalone stop between other appointments, and there is no public shortcut from the basilica.
Vatican City · YOUR QUESTION, ANSWERED
Is the Sistine Chapel inside St. Peter's Basilica?
No. The Sistine Chapel is inside the Vatican Museums, not St. Peter’s Basilica, and is reached only through the museums’ ticketed entrance on Viale Vaticano, about a 15-minute walk from St. Peter’s Square. The standard route through the museums to the chapel takes roughly 2–3 hours and several kilometers of walking. The museums are closed on Sundays except the last Sunday of the month, when entry is free and very crowded.
Sources & further readingVatican Museums: visitor information
Official sources cover institutional information. Suggested pacing and itinerary choices are planning guidance. Check current arrangements for your travel dates.