Question on International planes ...fullplane or not ?

You can most likely count on a mostly full coach section. I have seen seats open in Business Class and 1st class but coach is different.

In my experience, if your flying on the weekend the plane is usually full. There tends to be more open seats in the middle of week.

That's an impossible question to answer.

But answer this...why would an airline continue to fly a route if the planes were empty? They lose money.

If you're flying a US based carrier, you might be able to look at the seatmap for your flight to see how full it is but that will keep changing until the flight departs.

Almost everytime I've flown overseas it's been booked full. However, when I flew Detroit to London in November, there were probably 3 seats to every 1 passenger. It was great! Return flight was full though. I'd plan on having a pretty full flight.

It seems to be getting more and more crowded every year. The last few years that I have flown there have been very few empty seats.

In May we flew Delta to Venice and Delta back to Cincinnati from Rome at the end of the month. There were lots of open seats in coach. I moved to a whole center group of seats and my husband had 2. We also flew to Paris around October1 and came back Delta at the end of the month and many empty seats. We try to fly early in the week - Monday or Tuesday. I think there are more open seats earlier in the week.

Jane ...i'm going same route ecpect JFK to Venice and Rome to New York ...there are ton's of seats available on these planes right now ...unless they offer some cheaper fares there going to have alot of seats left

Another thing that I have found is they have a scheduled flight and their code share partner has one at almost the same time.Then if they dont have enough passengers for both they cancel one of them.

Patrick is asking a question about Logistics...
Whether a plane is full, half full or half empty depends on many factors. A few things to consider are whether you are flying with a Scheduled Carrier (ie: Air Canada or a Charter ie: Air Transat.) Seasonality, Tour Operator Blocks of Seats just to name a few.

Charters sometimes cancel flights to combine Passenger Loads if there isn't enough "Bums in Seats" as we call it. It's much more profitable to send one full Aircraft as opposed to two that are half empty.
Full flights the second and third week of May are typical given the season. That same flight might be 60% Full during low season.
A Flight might be showing as Full but in reality you could see empty seats. There are almost always No shows which are hopefully sold off to last minute travellers and Standbys. Tour Operators book a block of seats and release the unsold ones last minute. That's why the numbers can change quickly, especially with the Charter Carriers.

I flew to Paris on a Wednesday last month. The plane was only about half full. I was able to lie down in an almost empty center row and sleep.

My expereince is rarely are the planes not that full anymore. Airlines have gotten smarter and smarter about "yield management" and as the price of fuel goes up expect them to continue this trend. They just can't afford to fly that big jet half empty across the Atlantic.

I had three European trips last year. On ONE there was an empty seat next to me. (Middle section of a two/three/two layout) The FA was amazed since they were overbooked. I think the gate guys either messed up or everyone left was not a "party of one" (The gate agents may have been distracted by the woman who had checked two big bags and had FOUR huge carryons which they were not going to let her on with LOL!)