Jack London · 1876
Heavy going at CET-4 level. Not unreadable — just not readable the look-every-word-up way.
Coverage = the share of words in the text you already know. The research gives two lines: 98% before independent fluent reading is realistic, 95% for the instructional level that needs support (Hu & Nation, 2000). Proper nouns are not counted as unknown — recognising that it is a name is enough; this book has 349 of them.
Advanced — read it with glosses. 105,927 words in total; at 150 words a minute for a non-native reader, about 11 h 46 min to finish. Average sentence length 14.9 words. This book is heavy on rare, archaic and invented words: even 25,000 high-frequency word families will not reach 95% coverage — its difficulty is not in the common vocabulary.
The opening of The Sea-Wolf, word for word. Tap any word you don't know and its meaning here appears beside it — no sign-up, tap as often as you like.
I scarcely know where to begin, though I sometimes facetiously place the cause of it all to Charley Furuseth’s credit. He kept a summer cottage in Mill Valley, under the shadow of Mount Tamalpais, and never occupied it except when he loafed through the winter months and read Nietzsche and Schopenhauer to rest his brain. When summer came on, he elected to sweat out a hot and dusty existence in the city and to toil incessantly. Had it not been my custom to run up to see him every Saturday afternoon and to stop over till Monday morning, this particular January Monday morning would not have found me afloat on San Francisco Bay.
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Ordered by unknown words per 100. Lower reads easier; to step up a level, pick a higher number.
Computed by Readii from the public-domain text (updated 2026-10-21), not estimated by hand. The Readii reading level is our own scale, anchored on unknown-word density; it is not the same system as Lexile or AR and does not convert directly. Unknown words are measured against the CET-4 ∪ Gaokao lists, so this is difficulty for a Chinese-speaking learner, not a native-child reading level.