What Is Lexical Coverage?

Lexical coverage is the share of words in a text that you already know. If a 1,000-word article contains 20 words you don't know, your coverage is 98 percent. The concept matters because comprehension does not fall off gently: research shows that a few percentage points of coverage make the difference between reading comfortably and struggling through every paragraph.

What the coverage numbers feel like

Percentages near 100 sound similar, but they are not:

The research: 95% and 98%

Batia Laufer (1989) suggested 95 percent as the threshold for reasonable reading comprehension. Hu and Nation (2000) tested readers on a fiction text at different coverage levels and found that comprehension rose steadily with coverage, and that around 98 percent was needed for most readers to understand the text adequately without help. Laufer and Ravenhorst-Kalovski (2010) later proposed two thresholds: 95 percent as a minimal level and 98 percent as an optimal one.

Paul Nation (2006) then asked how many words are needed to reach 98 percent. His estimates:

• Novels and newspapers: about 8,000–9,000 word families
• Movies and conversation: about 6,000–7,000 word families

These figures usually assume that proper nouns (names of people and places) are known. Our guide on how many words you need to be fluent unpacks them further.

Why coverage matters for vocabulary learners

It explains the intermediate plateau

Because of Zipf's law, the first few thousand words raise coverage quickly, and then each additional thousand adds only a percentage point or so. A learner at 3,000 families may have about 90 percent coverage of a novel, which still means 30 unknown words a page. The jump from "I know most words" to "I can read this comfortably" takes thousands more.

It decides whether you can learn from context

Guessing words from context clues works when the surrounding words are known. At 98 percent coverage, each unknown word sits in a clear context. At 90 percent, the context itself is full of gaps. This is why extensive reading works best with texts at or above about 98 percent coverage, often achieved through graded readers.

How to use coverage in study

1. Test a text before committing. Count the unknown words on one page. More than 10–15 per 300 words means it is better as intensive study material than as pleasure reading.
2. Use a tool. The lexical coverage calculator estimates coverage for a pasted text; the vocabulary size estimator estimates your overall level.
3. Choose reading in your sweet spot: 95–98 percent for study, 98 percent and above for fluent reading.
4. Save the recurring unknowns. Words that appear several times in your reading are worth learning first. Wordie lets you save them as you read and highlights them on later pages.

Common mistakes

• Confusing types with tokens. Coverage counts running words, so one unknown word repeated ten times counts ten times.
• Assuming 98 percent means perfect understanding. Background knowledge, grammar and idioms still matter.
• Reading only far above your level. Texts at 85 percent coverage feel productive because you look up many words, but most of them won't stick.

Sources: Laufer, B. (1989), What percentage of text-lexis is essential for comprehension?; Hu, M. & Nation, P. (2000), Unknown vocabulary density and reading comprehension, Reading in a Foreign Language; Nation, P. (2006), How large a vocabulary is needed for reading and listening?, Canadian Modern Language Review; Laufer, B. & Ravenhorst-Kalovski, G. C. (2010), Lexical threshold revisited, Reading in a Foreign Language.