Jules Verne · 1828
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 721 of them.
Advanced — read it with glosses. 104,564 words in total; at 150 words a minute for a non-native reader, about 11 h 37 min to finish. Average sentence length 15.6 words. Reaching 95% coverage on this book (the floor for readability) takes roughly 20,500 word families.
The opening of Twenty Thousand Leagues under the Sea, 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.
The year 1866 was signalised by a remarkable incident, a mysterious and puzzling phenomenon, which doubtless no one has yet forgotten. Not to mention rumours which agitated the maritime population and excited the public mind, even in the interior of continents, seafaring men were particularly excited. Merchants, common sailors, captains of vessels, skippers, both of Europe and America, naval officers of all countries, and the Governments of several states on the two continents, were deeply interested in the matter.
For some time past, vessels had been met by “an enormous thing,” a long object, spindle-shaped, occasionally phosphorescent, and infinitely larger and more rapid in its movements than a whale.
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These are already built, and closest in difficulty to Twenty Thousand Leagues under the Sea.
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.