What makes text harder to read?

Two things matter most: how long the sentences are and how long the words are. Long sentences hold more ideas at once, and long words tend to be less common. Readability formulas turn these two measurements into a single number.

The Flesch-Kincaid Grade Level

This is the most widely used formula in schools. It gives you a U.S. school grade — so a score of 5 means an average fifth-grader could read the text. The formula is:

The first part rewards shorter sentences; the second part rewards shorter words. Add them up and you get the grade level.

The Flesch Reading Ease

This related score runs from 0 to 100, where higher means easier. A score of 60–70 is plain English that most people read comfortably; below 30 is very difficult, university-level text.

Use the scores wisely

Readability formulas only measure sentence and word length. They cannot judge interesting ideas, clear organisation or background knowledge. Treat the score as a useful signal, not the final word.

Check your own text

Paste any passage into our Reading-Level Checker — it shows every number that goes into the formula, so you can see exactly how the level is worked out.