Almost every Europe itinerary we are asked to fix has the same problem: too many cities. Adding a city costs you most of a day in transit and packing, and it takes those hours from the places you actually came to see.
Here is what we consider a realistic minimum, based on what people regret when they cut it shorter.
Paris — three nights minimum, four if there are children
Two nights means one full day, which means the Eiffel Tower and the Louvre and nothing else. Three gives you the landmarks plus Montmartre and an evening on the river. Four is necessary if Disneyland or Versailles is on the list.
Rome — three nights
The Vatican is essentially a full morning. The Colosseum and Forum are another. That leaves one day for the Pantheon, the Trevi Fountain and simply walking, which is the best thing to do in Rome anyway.
Venice — one night, and stay overnight
Venice is small, and a day is enough to see it. But the city transforms after the day-trippers leave, and the difference between a Venice day trip and a Venice night is the entire point.
Florence — two nights
One full day covers the Duomo, the Accademia and Piazzale Michelangelo. A second lets you add the Uffizi properly or take a half-day into Tuscany.
Switzerland — four nights minimum
Not per town — total. The mountain excursions each take a full day and are weather-dependent. Two excursions from two bases with a spare day is the realistic minimum, and the spare day is not optional if you care about seeing Jungfraujoch in clear weather.
Amsterdam — two nights
A canal cruise, the Rijksmuseum or Van Gogh Museum, and the Jordaan on foot. Three if you want Keukenhof in spring or Zaanse Schans.
London — four nights
The museums alone could absorb a week, and they are free. Four nights covers the landmarks, one or two museums, a show and a day trip.
Prague, Vienna, Budapest — two nights each
All three are compact and walkable. Two nights each in all three, connected by train, makes an excellent ten-night trip.
The arithmetic
If you have ten nights, that is realistically three cities plus Switzerland, or four cities without it. Not seven. Every itinerary we have seen with seven cities in ten nights produced a traveller who came back tired and remembered mostly the coach.
One more thing
Take trains, not internal flights, anywhere in Western Europe. City centre to city centre, no airport security, and you keep the two hours that flying quietly takes from you at each end.