As I was developing my career and skills as a writer, I needed to learn some of the quantitative aspects of the work. Writing, as it turns out, is more than just putting words together well, but also about putting in the RIGHT amount of words. This might be foreign to people who write mostly "to the drawer" or self-publish, but any kind of commercial writing work has a framework that needs to be adhered to. For example, if you write an article for a newspaper, you can't just write until you feel the topic is covered. Newspapers have a finite size, and each editor is allotted a quota of pages (or space on a page). Then, when they ask their writers for an article, they would ask for a certain length, to which the writer must stick to, just like a carpenter would need to adhere to the client's specifications when building a cabinet or couch. Usually, there is some leeway, so if the editor asked for 500 words, a writer can submit 550 (even 600 if there is a good relationship with the editor, or if the writer is highly reputable) and the editor would either squeeze it in, or edit it down to the right size.
To the aspiring or new writer, I would strongly advise to be super precise with word count, because if you submit 600 words and the editor needs to cut out 100 words, you will have no control over which changes they will make. The more you go over-board, the higher the risk of something becoming less clear, or even incorrect. By being more precise, you can increase the likelihood of your work being presented as-intended, and it will also present you as more professional to your boss, and build yourself a good reputation.
When dealing with other sorts of media, there are other ways of measuring volume. For example, if you are doing a presentation, you might be asked for a "1 academic hour" presentation. If doing comedy, you might be asked to generate material for "3 minutes". If you are writing a script, you might be required to write one for a "half hour" show. If you wondered how these translate into word counts or other counts. Here are some facts on the topic.
Books and novels
A young-adult novel will run between 20,000 and 40,000 words. That would also be the length of a novella in mainstream fiction. A typical page of a paperback novel will run around 400 words, while a typical page in a default page in Microsoft word is about 500 words (that is, with a default font setting of Calibri 11, and a 1" margin on all sides).
A mass-market western, mystery or SF novel used to run to 60,000-70,000 words, which results in a 150-200 page book. However, nowadays they're more likely to hit 90,000 words. Fantasy novels are frequently about 125,000 words per volume. Mainstream fiction would be about 55,000 words.
Technical books are all over the place, often reaching 800 pages (average is 400-500 pages) but their word-count is usually 15-20% less than other types of literature due to a high number of screenshots and illustrations, as well as lengthy index sections. On the other hand, their page-size is larger, so keep your aim at 400 words per page of "final" content.
Movies and TV
Scripts are written very differently, because the guiding principle is screen-time. Scripts contain a lot of background info, like descriptions of action or of the scene itself, which aren't spoken words. For a screenplay, a page would typically result in 1 minute on-screen, so for a "half-hour" TV show (which would be 21-23 minutes "net" without commercials and start/end credit sequences) would require a 20-25 page script. However, just like any other media, more content is produced than is needed, so a half-hour script can often be almost twice that size.
In a typical script, you would have about 125 words per-page, as the language represent normal dialog which has relatively short sentences. A script also needs to have large margins for the actors to take notes. A "feature" movie can run anything from 80 minutes to 135 minutes, with many directors being self-indulgent and producing movies that cross the 2.5 hours mark. A 2.5 hour movie would require a 150+ page script with close to 20,000 words.
Radio and public-speaking
The average person speaks at somewhere between 125 and 150 words per minute, so when producing content for a radio or public speaking, that's the numbers that should guide you.
Be wary of over-cramming content into presentations, in case you are preparing a slide-deck to accompany a presentation. The slide-deck is not supposed to contain everything you are going to say, but the opposite - a slide supports your words, so you should only write down key words or short phrases (some places have even been know to ban slides completely). A slide-deck would typically include 1 slide per 2 minutes of presentation time, and contain no more than 40 words per slide. The best speakers out there often have 2-6 words per slide, thus making sure the audience is focused and listening to THEM, rather than trying to catch-up to what's on-screen. Some world-leading presenters avoid words altogether and just have images and graphics up there.
Keep in mind that an average adult can read about 200 words per minute (with College students clocking-in at around 300 WPM). Many people aren't mentally able to "let go" and keep cramming text into their slides, but if you are able to produce high-quality (= low word count) slides, you can get-away with as much as a slide per minute. It's always a good idea to cut your content by 15% to leave time for Q&A. Also, keep in mind that in many places an "hour" of presenting actually means only 45 minutes (also known as an "Academic hour").
If you like to be fully prepared, or if it's a topic you never presented before, it's not a bad idea to write-out your full text, factoring in around the number above (125-150 spoken words per minute). Naturally, you can't read off-the-page while presenting, so a good idea is to convert the text into a bulleted-list, with each bullet item only 2-5 words to remind you what it's about, and representing about 1-2 minutes of actual speech.
Telling jokes goes around the same rate as public-speaking (125-150 WPM), but writing jokes is even more precise than other types of writing. Well-established comedians like Jerry Seinfeld or Jay Leno can afford to tell a "story"-type joke, which would go on for a few minutes until the punch-line is reached, but unknown comedians need to work harder to keep their audience engaged. For such, a joke should be about 30-50 words long, taking about 15-20 seconds to tell.
Some comedians use the term "LPM" or Laughs-per-Minute to measure the quality of their material. A good guideline for LPM is to aim for 4-6 LPM. That doesn't necessarily mean you need to tell six 10-second jokes every minute, but a single joke can include more than one "laugh". For example:
"My company is interviewing people this week, and my boss told me that if I'm interviewing a woman, I can't take pictures of her during the interview. Isn't that unbelievable??? Like…we are interviewing WOMEN now???"
The above joke is 35 words long (15 seconds), but it actually has 2 laugh points - one at "during the interview" and a second at the end of the joke. If all your jokes are at that level, you could reach 8 LPM, which is fantastic. The numbers above do mean that a 1-hour comedy show, which is the average for most shows, would require you to write, organize and memorize up to 240 jokes.
If you are wondering how one remembers so much material…it's not easy. With most comedians writing their own material, they would typically remember the joke, but they might not remember which jokes they want to include and in what order. However, when you see a tapes comedy show on TV, that would typically be recorded after the comedian has toured with the show for months, giving them time to both iron-out the kinks, and memorize the sequence. Often the show is recorded several times and then edited together to eliminate jokes that fell flat, or audience heckling, etc.
During the period of preparing for a taping, some comedians would use a simple notebook or sheet of paper to help remember. Some use their phones or write stuff on their own hands. Some write or print stuff in large fonts and tape it to the floor, so they can glance down and read it. A trick I myself usually use is taping a list of jokes on a water bottle (which I either carry in my hand, or place on the customary stool that most comedy stages have). The bottle can also be used as a prop for some stories. Like in presenting, it's important to be able to summarize a joke into a 1-3 word phrase that you can read quickly and be reminded of what it is.