The Flesch Reading Ease score explained
What the 0 to 100 Flesch Reading Ease number means, the bands behind it, and how word and sentence length move it up or down.
Where the score comes from
Rudolf Flesch published the Reading Ease formula in 1948 to put a single number on how hard a passage is to read. It weighs just two things: the average number of words in a sentence and the average number of syllables in a word. The full equation is 206.835 minus 1.015 times words per sentence minus 84.6 times syllables per word. Because syllables per word carries the heavier coefficient, vocabulary choice moves the score more than sentence length does.
Reading the bands
The raw number maps onto plain-English bands. Ninety and above is very easy, eighty to ninety is easy, seventy to eighty is fairly easy, and sixty to seventy is standard prose that most adults read comfortably. Fifty to sixty is fairly difficult, thirty to fifty is difficult, and anything below thirty is very confusing and usually needs a specialist reader. Most mainstream news and marketing copy aims for sixty or higher so it stays accessible.
Why the number can leave the 0 to 100 range
People often assume the score is capped, but the formula is open ended. A run of blunt three-word sentences made of single-syllable words can push the result above 100, while a single long sentence stuffed with polysyllabic terms can drive it below zero. This tool reports the true value rather than clamping it, because those extremes are honest signals: a negative score is a strong hint that the passage is far too dense for a general audience.
Raising a low score
Two levers control the number. First, split long sentences; every sentence you break in two lowers words per sentence and lifts the score. Second, reach for shorter words, since the syllable term dominates the math. Reading the passage aloud surfaces the sentences that run out of breath and the words that stumble. Retest after each edit and you can usually move a dense draft from the thirties up into the readable sixties without losing meaning.