Free self-guided itinerary. This is a travel guide, not a bookable guided tour.
One day is not enough to see Paris, and this guide does not pretend otherwise. Instead of a list that cannot be completed, it offers three realistic shapes for the day and is honest about what each one gives up.
Centre-led. The islands, the river, the Left Bank. Best if it is your first time and you want the shape of the city rather than its interiors. Gives up: museums.
Museum-led. One major collection in the morning, a garden after lunch, a neighbourhood in the evening. Gives up: distance covered.
Neighbourhood-led. Two districts, properly, on foot. Best if you have been before. Gives up: the landmarks.
Three of them, and they are always the same. Squeezing three major museums into one day, so that by the third nobody is looking at anything. Crossing the city end to end more than once. And not checking which day of the week your museum is closed — it is not the same day everywhere, and this is the single most common planning error in Paris.
This plan is set out as morning, afternoon and evening rather than hour by hour. Minute-level itineraries collapse at the first delay, and there is always a first delay.