Readability

How the Flesch Reading Ease score is calculated

The Flesch Reading Ease formula, developed by Rudolf Flesch in 1948, produces a score between 0 and 100: RE = 206.835 − (1.015 × average words per sentence) − (84.6 × average syllables per word). The two drivers are sentence length and syllable count. Longer sentences and more polysyllabic words push the score down (harder to read); shorter sentences and simpler words push it up.

The scoring ranges are practical landmarks. 90–100: very easy (Simple English, children's books). 70–80: easy (plain English, suitable for general consumer audiences). 60–70: standard (plain writing, appropriate for most web content). 50–60: fairly difficult (high school level). 30–50: difficult (college level, academic writing). 0–30: very difficult (professional or technical writing, legal documents).

For most online content — websites, email newsletters, product pages, help articles — aim for 60–70. Marketing copy often targets 70+. Journalism traditionally targets 65–70 (the "newspaper standard"). Academic papers routinely fall below 30, which is appropriate for their audience but would drive away general readers.

Gunning Fog and SMOG — which score to trust for your content

The Gunning Fog Index was developed by Robert Gunning in 1952 for newspaper publishers who wanted to ensure their content reached a broad audience. The formula: Grade = 0.4 × (average words per sentence + percentage of words with 3+ syllables). It targets US school grade level — a score of 8 means an 8th-grade reading level (13–14 year olds).

SMOG (Simple Measure of Gobbledygook) was developed by G. Harry McLaughlin in 1969 and is calibrated specifically on reading comprehension — not just decoding ability. Research suggests it is the most accurate predictor of whether readers actually understand content, especially in health and medical contexts. The US CDC and many health agencies use SMOG as their primary readability measure because health literacy is lower than reading ability; patients can decode words they don't comprehend.

For general web content, Flesch Reading Ease is the most commonly reported score. For health, medical, or public health content where true comprehension matters, SMOG is more appropriate. Gunning Fog is a good middle ground that weights both sentence length and complex vocabulary.

Practical tips for improving your readability score

The two biggest levers are sentence length and word choice. Most readability formulas weight these roughly equally.

For sentences: aim for an average of 15–20 words per sentence for online content. Sentences over 30 words are almost always improvable by splitting at a conjunction or semicolon. Vary length — too many identical-length sentences feel monotonous. Short sentences (under 10 words) create emphasis; use them after complex sentences.

For word choice: prefer a shorter, everyday word over a longer, technical one when both are accurate. "Use" instead of "utilise". "Help" instead of "facilitate". "End" instead of "terminate". "Show" instead of "demonstrate". This is not dumbing down — it is respecting the reader's time. Technical jargon is fine when writing for a specialist audience that shares vocabulary; define terms on first use when writing for a general audience.

For structure: active voice keeps sentences shorter and clearer than passive voice. "The system processed your request" (6 words) vs "Your request was processed by the system" (7 words, and the agent is buried at the end). Bullet points and subheadings break up long blocks of prose and let readers scan — which is how most people read online.