Yoast sentence length: 20 words, 25 percent, and why

Two numbers, not one

The check combines a length limit with a share:

1. The limit decides which sentences count as long. In English and most languages it is 20 words. Catalan, Spanish, Farsi, Italian and Portuguese allow 25 words, Hebrew, Russian and Turkish use 15, and Japanese is measured as 40 characters.
2. The share decides the traffic light: 25 percent or fewer long sentences is green, between 25 and 30 percent is orange, and above 30 percent is red. Cornerstone content moves the green line to 20 percent, and Polish uses tighter bands of its own.

The feedback names both: "32% of the sentences contain more than 20 words, which is more than the recommended maximum of 25%. Try to shorten the sentences." When you pass, it simply says "great!", and the highlight button shows which sentences were counted as long.

So a text can include plenty of 35 word sentences and still be green, provided most of its sentences are shorter.

The working memory argument

Yoast's reasoning is that readers hold the words and relationships of a sentence in working memory until the sentence ends. The more clauses you stack, the more they have to juggle before the meaning arrives. That is especially true for readers in a second language, readers with cognitive or reading difficulties, and anyone reading on a small screen where a long sentence spans many lines.

The same idea runs through plain-language writing guidance, including the guidelines used by US federal agencies under the Plain Writing Act of 2010, which favor short sentences as one of the most reliable ways to make text easier to understand. Yoast's 20 word figure is a practical threshold rather than a research constant, and the per-language limits reflect that some languages naturally use longer sentences.

Long sentences that earn their place

Not every long sentence is a problem. Some are long because they carry a precise condition that would be ambiguous if split: "If your host caches pages at the server level, clear that cache after you change the permalink structure, or visitors may keep seeing the old URLs." Breaking that into three sentences can separate the condition from the action.

Legal text, academic writing and detailed technical explanations will often exceed the share for good reasons. A few long sentences also give prose rhythm; a text made entirely of short sentences reads as clipped.

Take the red light seriously on pages for broad audiences, such as help articles, product pages and beginner guides, and be relaxed about it on specialist content.

Shortening without choppiness

Most overlong sentences can be fixed with a few moves:

• Split at the joins. "And", "which", "while" and semicolons often mark where one sentence can become two.
• Turn series into lists. A sentence listing four settings reads better as four bullets.
• Cut the throat-clearing. "It is important to note that" and "In order to" add words without meaning.
• Put the point first. "To fix it, clear the cache" is shorter and clearer than a sentence that builds up to the instruction.

After editing, read the passage aloud. If every sentence is now the same length, merge one or two back together. The goal is a mix, mostly short to medium, with an occasional long sentence where it helps.

Average versus share: how Hydrogen SEO measures it

Hydrogen SEO measures sentence length differently. The readability part of its SEO score uses the average words per sentence: 20 points minus 0.4 for each word in the average sentence, so 15 words scores 14 points and 25 scores 10.

The two methods can disagree. A post made entirely of 18 word sentences passes Yoast's check, since none cross 20 words, but its average of 18 earns 12.8 of 20 points in Hydrogen. A post with mostly 8 word sentences and a handful of 40 word ones may fail Yoast's share while scoring well on Hydrogen's average. Neither is wrong; they are different summaries of the same text.