Two formulas, one set of counts
Flesch–Kincaid Grade Level uses the average words per sentence and syllables per word to estimate a US school grade. Flesch Reading Ease uses the same two ratios with different weights. Reading Ease rises as the measured text becomes easier. Grade Level rises as the measured text becomes more demanding.
Paste at least 100 body words and three sentences to see both document scores. The working panel shows the exact counts. It displays the ratios rounded to four decimals and uses the exact fractions in the equations, so you can reproduce the result without rounding early.
Work a score by hand
Suppose an English passage has 100 words, five sentences and 150 syllables. That is 20 words per sentence and 1.5 syllables per word.
0.39 × (100 ÷ 5) + 11.8 × (150 ÷ 100) − 15.59 = 9.91
206.835 − 1.015 × (100 ÷ 5) − 84.6 × (150 ÷ 100) = 59.635 ≈ 59.64
This example uses invented counts to illustrate the arithmetic. The calculator runs the same equations on your own counts. It shows the calculated values, which can fall outside familiar grade or Reading Ease ranges.
Interpret the scores in context
Grade 10 roughly indicates the level of text associated with tenth grade in the US. It gives you a starting point for reviewing a passage. A Reading Ease result near 60 can be a reasonable comparison point for general English prose. A specialist audience may be comfortable with a more technical passage because its vocabulary is familiar.
Look at the counts by sentence when two drafts have similar grades. A single long sentence with several conditions can get lost in an average. Ask a reader to explain the most important instruction after reading it once.
Why two calculators can disagree
Different tools may count “well-known” as one or two words, handle abbreviations differently, or estimate a syllable differently in a name. Concise identifies explicit headings and some standalone title lines, and excludes those from its body-text calculation. Small passages magnify any difference in a count.
Compare revisions in the same tool. If a score gives you a reason to revise, use the full readability checker to find longer sentences or wording worth reviewing. The methodology page explains the shared formula and the way the editor displays a rounded headline grade.
Microsoft Word readability formulas · Kincaid and colleagues, 1975