I know that the Louvre is free the first Sunday of every month. Does anyone know if the crowds are worse then than on an average day at the beginning of May? Thank for the help.

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Crowds are bad on Sundays, and even worse than that on free Sundays.

In my experience, museums are very crowded on free days. Really crowded.
We went to the Rodin Museum not knowing it was a free day, and the line to go through the house was very long. We went through at near closing time after wandering the gardens.

Crowds at the Louvre almost get impossible because the throngs around the best known works are very large.

Mona Lisa draws a crowd even on normal days. On free days, she is surrounded on 3 sides by throngs 9 to 10 people deep.

I'm sure there are many portions of the Louvre that are quite empty during free Sundays. It's a very large museum and people are crowding around the "top 10" works of art. Last time I was there Mona and Venus were inundated with viewers however the Marley court was almost empty as was the Napoleon III rooms.

Take a virtual tour of the Louvre and choose some galleries that interest you. If one is crowded you can go on to another and still enjoy the art without throngs of people.