How readable is your writing, really?
Readability scores answer one question: what reading level does this text demand? The answer matters because the gap between "what I write" and "what my audience reads" is where comprehension dies. A medical brochure aimed at the general public but written at college level helps no one. A technical white paper aimed at engineers but written at 6th grade insults them.
Six classic formulas tackle this problem from different angles. They mostly agree, which is the whole point of running all of them — when five say "8th grade" and one says "12th," the outlier is suspect, not the consensus.
Flesch Reading Ease — the headline number
The Flesch Reading Ease score, published by Rudolf Flesch in 1948, returns a number between 0 and 100. Higher is easier to read. The scale was calibrated against US Navy training manuals and remains the most widely-cited readability metric.
A few benchmarks to anchor the scale:
- 90–100 — easily understood by an average 11-year-old. Children's books, simple instructions.
- 80–90 — easy. Easy reading, plain prose.
- 60–70 — standard. Most newspapers and magazines target this range. The Wall Street Journal hovers around 65.
- 30–50 — difficult. Academic articles, complex business writing.
- 0–30 — very difficult. Legal documents, scientific papers, government regulations.
Microsoft Word's built-in readability check uses Flesch Reading Ease, which is why most people who care about readability quote the Flesch number first.
Flesch-Kincaid Grade Level — same formula, different scale
The Flesch-Kincaid Grade Level rearranges the same inputs (sentence length, syllable density) into a US grade level. So a Flesch-Kincaid Grade of 8.5 means "an average 8th-grader can read this." It's the same information as Flesch Reading Ease, just scaled to the metric most non-academics intuit ("8th grade" is more legible than "score 65").
Gunning Fog — the "complex words" formula
Robert Gunning's 1952 Fog Index introduces a different signal: the proportion of words with three or more syllables. The idea is that long words are harder, regardless of sentence length. Gunning Fog returns a US grade level. A Fog of 7 is conversational; a Fog of 12 is high school; a Fog of 17+ is academic.
SMOG — the medical-literature standard
SMOG ("Simple Measure of Gobbledygook"), developed by G. Harry McLaughlin in 1969, focuses on counting complex words across a 30-sentence sample. It's the formula most often used in medical and public-health writing because of its bias toward identifying technical vocabulary that confuses non-specialist readers.
SMOG specifically requires 30+ sentences for its published accuracy. For shorter text, the score is directional but not precise.
Automated Readability Index — the character-based approach
The ARI ditches syllable counting entirely and uses character counts instead. Developed for the US Air Force in 1967, it's the easiest formula to compute mechanically (no syllable heuristic needed) and works well as a sanity check on the syllable-based scores.
Coleman-Liau — designed to be hand-computed
The Coleman-Liau Index, like ARI, uses character counts instead of syllables. It was specifically designed in 1975 to be computable by hand from raw newspaper text without complex linguistic analysis. The trade-off is that very short sentences with long words can throw it off — outliers in the per-formula breakdown often originate here.
What grade level should I aim for?
The honest answer: whatever your audience reads. There's a tempting "lower is better" instinct that runs through readability advice, but it isn't quite right.
- Children's content — grade 3–5
- General-public web content — grade 7–9 (this is the sweet spot for most blog posts)
- News journalism — grade 9–11 (NYT targets ~9, WSJ ~11)
- Business writing — grade 10–12
- Technical / professional — grade 12–14
- Academic — grade 14–18
Hemingway scored about grade 4 in his fiction. Scientific journals run grade 14–18 because the audience expects it. Match your audience, not a universal target.
How to lower grade level fast
If your draft is reading at grade 14 and your audience is grade 8, three changes drop the score quickly:
- Shorten sentences. A long sentence is the single biggest contributor to high grade level. Aim for an average of 15–20 words per sentence in general-audience writing.
- Replace polysyllabic words. "Utilize" → "use." "Demonstrate" → "show." "Sufficient" → "enough." Each multi-syllable word swap drops the syllable density.
- Break compound thoughts. A single sentence with three clauses becomes three sentences with one clause each. Easier to parse, lower grade level.
The reverse also holds: to raise the grade for technical audiences, write longer sentences with precise vocabulary. The audience expects precision more than easiness, and over-simplifying technical content insults the reader.