QUESTION: What is the correct length of a paragraph and a sentence when you are writing fiction?
There is no average length for paragraphs, but a really long paragraph is off-putting to the eye on paper and even more off-putting when you are scrolling on a small screen so shorter paragraphs have become the norm for current narrative.
When the average person looks at a page, they want to see some space, not a massive block of text.
The best way to do paragraphs, as a writer, is to vary the paragraph lengths on the page.
I go into much more detail about paragraph lengths in this blog entry.
The same is true of sentence length.
Both sentence and paragraph length are also influenced by what is being written. A narrative description can have a longer length for both, but an action scene would have a shorter length for both.
Some writing teachers suggest varying between long sentences and short sentences in the same paragraph.
Long sentences are good for leisurely story pace. Short sentences are perfect for action scenes.
If you are unsure about how your sentences work with your content, read the sentences aloud. Sentence problems usually show up while doing this.
A good critique partner helps, too.