Sorted after counting, never before
Hardest books to read
Ranked by Flesch–Kincaid grade level. Topped by Fifteen Thousand Useful Phrases at grade 70.8.
SOURCE·Project Gutenberg full texts·50 of 683 measured texts ranked·REVIEWED JUL 2026
The first fifty, measured
| # | Book | Author | books to read | Reading time |
|---|---|---|---|---|
| 1 | Fifteen Thousand Useful Phrases | Kleiser, Grenville | grade 70.8 | 11 min |
| 2 | The History of Don Quixote, Volume 1, Complete | Cervantes Saavedra, Miguel de | grade 26.6 | 14h 24m |
| 3 | Don Quixote | Cervantes Saavedra, Miguel de | grade 26.4 | 28h 36m |
| 4 | The Decameron of Giovanni Boccaccio | Boccaccio, Giovanni | grade 25.5 | 20h 31m |
| 5 | Utopia | More, Thomas, Saint | grade 24.1 | 2h 54m |
| 6 | The Sceptical Chymist | Boyle, Robert | grade 23.8 | 5h 54m |
| 7 | The Expedition of Humphry Clinker | Smollett, T. (Tobias) | grade 21.9 | 9h 56m |
| 8 | A Modest Proposal | Swift, Jonathan | grade 20.9 | 14 min |
| 9 | In Praise of Folly | Erasmus, Desiderius | grade 20.7 | 2h 59m |
| 10 | The Life and Adventures of Robinson Crusoe | Defoe, Daniel | grade 20.6 | 8h 05m |
| 11 | The life and opinions of Tristram Shandy, gentleman | Sterne, Laurence | grade 19.9 | 12h 35m |
| 12 | The Adventures of Ferdinand Count Fathom — Complete | Smollett, T. (Tobias) | grade 19.7 | 10h 47m |
| 13 | Paradise Lost | Milton, John | grade 19.6 | 5h 20m |
| 14 | Plutarch | Plutarch | grade 19.5 | 49h 22m |
| 15 | The Birth of Tragedy | Nietzsche, Friedrich Wilhelm | grade 19 | 3h 37m |
| 16 | Essays of Michel de Montaigne — Complete | Montaigne, Michel de | grade 18.5 | 35h 02m |
| 17 | The Adventures of Roderick Random | Smollett, T. (Tobias) | grade 18.4 | 12h 46m |
| 18 | The Countess of Pembroke's Arcadia | Sidney, Philip | grade 18.4 | 22h 57m |
| 19 | Royal Edinburgh | Oliphant, Mrs. (Margaret) | grade 18 | 10h 34m |
| 20 | Memoirs of the Court of Queen Elizabeth | Aikin, Lucy | grade 18 | 17h 47m |
| 21 | A System of Logic, Ratiocinative and Inductive | Mill, John Stuart | grade 16.7 | 27h 17m |
| 22 | Lives of the Most Eminent Painters Sculptors and Architects, Vol. 01 (of 10) | Vasari, Giorgio | grade 16.6 | 5h 51m |
| 23 | The Prince | Machiavelli, Niccolò | grade 16.5 | 3h 19m |
| 24 | Beyond Good and Evil | Nietzsche, Friedrich Wilhelm | grade 16.5 | 4h 11m |
| 25 | A Practical View of the Prevailing Religious System of Professed Christians, in the Middle | Wilberforce, William | grade 16.5 | 6h 59m |
| 26 | Gulliver's Travels into Several Remote Nations of the World | Swift, Jonathan | grade 16.4 | 7h 00m |
| 27 | The Pirate | Scott, Walter | grade 16.3 | 13h 12m |
| 28 | Leviathan | Hobbes, Thomas | grade 16.3 | 14h 09m |
| 29 | On the Nature of Things | Lucretius Carus, Titus | grade 16.2 | 4h 55m |
| 30 | The Life of George Washington, Vol. 4 | Marshall, John | grade 16.2 | 8h 10m |
| 31 | Hypnerotomachia | Colonna, Francesco | grade 16.1 | 4h 34m |
| 32 | Antiquities of the Jews | Josephus, Flavius | grade 16 | 36h 05m |
| 33 | History of Tom Jones, a Foundling | Fielding, Henry | grade 15.7 | 23h 25m |
| 34 | Under the Red Dragon | Grant, James | grade 15.5 | 10h 05m |
| 35 | Don Juan | Byron, George Gordon Byron, Baron | grade 15.4 | 8h 25m |
| 36 | Confessions of an English Opium-Eater | De Quincey, Thomas | grade 15.3 | 2h 34m |
| 37 | The Legend of Sleepy Hollow | Irving, Washington | grade 15.1 | 49 min |
| 38 | Biographia Literaria | Coleridge, Samuel Taylor | grade 15 | 9h 14m |
| 39 | The Book-Hunter | Burton, John Hill | grade 15 | 8h 48m |
| 40 | Mademoiselle de Maupin, Volume 1 (of 2) | Gautier, Théophile | grade 14.8 | 4h 35m |
| 41 | An Inquiry into the Nature and Causes of the Wealth of Nations | Smith, Adam | grade 14.8 | 25h 14m |
| 42 | My Life — Volume 1 | Wagner, Richard | grade 14.7 | 14h 40m |
| 43 | The Mysteries of Udolpho | Radcliffe, Ann Ward | grade 14.7 | 19h 28m |
| 44 | Herman Melville | Mumford, Lewis | grade 14.6 | 8h 07m |
| 45 | Baron Trump's Marvellous Underground Journey | Lockwood, Ingersoll | grade 14.5 | 4h 38m |
| 46 | The loyalists of America and their times | Ryerson, Egerton | grade 14.4 | 15h 16m |
| 47 | The Life of George Washington, Vol. 2 | Marshall, John | grade 14.4 | 8h 37m |
| 48 | Standish of Standish | Austin, Jane G. (Jane Goodwin) | grade 14.4 | 7h 45m |
| 49 | On the Origin of Species By Means of Natural Selection | Darwin, Charles | grade 14.4 | 10h 20m |
| 50 | Creative Evolution | Bergson, Henri | grade 14.4 | 8h 49m |
Ranked over the 683 texts measured here, not over everything ever printed — a ranking is only as wide as its shelf. The whole shelf, A to Z.
