The length of a script is determined by the number of pages rather than the amount of words in conversation. The regulation is one page per film minute. So, if a movie is released to critical and popular acclaim with a running time of 80 minutes, then it must contain eight pages.
However, it's not uncommon for movies to be longer or shorter than this minimum requirement. In fact, the average length of a movie today is about 87 minutes. This is because producers want to include more material that will appeal to audiences who don't want to watch a straight shot-by-shot adaptation of the book they're reading or game they're playing.
Some books and games are so iconic that even though they're only a few pages long, people think they deserve their own slot in cinema or gaming culture. For example, here are some famous shorts that have been turned into movies:
• The Wizard of Oz (1939) - 7 minutes
• Pinocchio (1940) - 8 minutes
• Fantasia (1940) - 12 minutes
• Dumbo (1941) - 15 minutes
The dialogue in the screenplay has no bounds. The only limitation is the number of pages, which should not exceed roughly 120, which is why, on average, and I emphasize this, works out to around one minute of screen time each page. A lot can be said about the length of scenes, but for now we will stick with minutes.
There are some exceptions though, like if the scene involves just one character talking to themselves out loud. In that case you can have as much dialogue as you want between these two elements.
Generally, a script is divided into chapters, which are usually between 10 and 20 pages long. There are ways to divide up the script without using chapters, but most writers I know prefer them as divisible units that are easy to write (and break down) into equal parts.
The more dialogue there is in a screenplay the faster it will be read by an audience member. This is because dialogue takes up space on the page and less space means more words per page. So, generally, the more dialogue there is in a screenplay the shorter the play will be.
However, there are times when including a lot of dialogue could actually make the story longer instead of shorter. This depends on how much people talk about what happens in the scene vs how well the scene is written.
Traditionally, a feature script is between 95 and 125 pages long. Scripts in Hollywood these days are rarely greater than 114 pages. Comedy scripts are often shorter than drama screenplays. A typical screenplay is used to market a film idea or full story treatment. The script is then revised by the writer or writers based on feedback from producers, directors, and actors.
A movie script is usually written before there is any intention of making the film. It is done this way because without a clear picture of what will be required to make the film, it's difficult to estimate how much time it will take. In most cases, a script will be written before there is even an agreement to make the film. If the producer does not like the script, he or she will most likely find another one. If they like it, they may ask the writer to revise it until they are satisfied with its quality. Of course, this all depends on the budget and the level of commitment shown by the producer.
The script is then sent out to directors, actors, and other artists who would be involved in the film. They give their opinion on whether they think it's worth pursuing and if so, how much time it might take. From there, you can expect to hear back if they want to work with you on the project.