Grade Level Readability Calculator
Score the reading difficulty of any text using four professional readability formulas — Gunning Fog, Flesch-Kincaid, SMOG, and Coleman-Liau. Use it to ensure your content matches your audience's expected reading level before publishing.
About this calculator
Readability formulas estimate the U.S. school grade level a reader needs to comfortably understand a piece of text. Each formula weighs sentence length and word complexity differently. The Gunning Fog Index is: 0.4 × ((words / sentences) + (100 × (complexWords / words))). The Flesch-Kincaid Grade Level is: 0.39 × (words / sentences) + 11.8 × (syllables / words) − 15.59. The SMOG Grade is: 1.043 × √(complexWords × (30 / sentences)) + 3.1291. The Coleman-Liau Index substitutes character counts for syllables: 0.0588 × ((words / sentences) × 100) − 0.296 × (sentences / words) − 15.8. A score of 8 means an 8th-grade reading level. Most general-audience web content targets grades 6–9; medical or legal documents often score 12–16. Lowering average sentence length and replacing polysyllabic words are the two fastest ways to reduce your score.
How to use
Take a passage with 100 words, 5 sentences, 150 syllables, and 15 complex words (3+ syllables). Using the Gunning Fog formula: Fog = 0.4 × ((100 / 5) + (100 × (15 / 100))) = 0.4 × (20 + 15) = 0.4 × 35 = 14.0 — equivalent to a college sophomore reading level. Using Flesch-Kincaid: Grade = 0.39 × (100 / 5) + 11.8 × (150 / 100) − 15.59 = 7.8 + 17.7 − 15.59 = 9.91 — about 10th grade. The two formulas differ because Flesch-Kincaid weights syllables while Gunning Fog weights complex word proportion.
Frequently asked questions
What is a good Flesch-Kincaid grade level score for a blog post or website?
For most general-audience blogs and marketing websites, a Flesch-Kincaid grade level of 6–8 is ideal — roughly the reading level of a middle schooler. This range is accessible to the widest adult audience without feeling condescending. News sites like the Associated Press target grade 8–10, while academic journals often land above grade 14. If your score is above 10 for a consumer-facing page, try shortening sentences and replacing jargon with simpler synonyms.
How does the SMOG formula differ from the Gunning Fog Index for measuring readability?
Both formulas focus on complex words (those with three or more syllables) but differ in how they weight sentence structure. SMOG uses the square root of polysyllabic word density scaled to 30 sentences, making it particularly reliable for health and medical communications — it was specifically validated against patient education materials. Gunning Fog applies a straight linear combination of average sentence length and complex word percentage, making it more sensitive to sentence length variation. For most general content, the two scores are within 1–2 grade levels of each other.
Why do different readability formulas give different grade level scores for the same text?
Each formula was developed and validated on different corpora and with different definitions of 'difficulty.' Flesch-Kincaid counts syllables as a proxy for word complexity; Coleman-Liau uses character counts; SMOG and Gunning Fog count words with three or more syllables. A text with many long but phonetically simple words (e.g., 'information,' 'conversation') will score differently across formulas than one with short but rare words. Using two or three formulas together and averaging the results gives a more robust and defensible readability estimate than relying on any single score.