SMOG index calculator — gold standard for medical and health text

The formula

SMOG = 1.043 × √(polysyllabic_words × 30 / sentences) + 3.1291

SMOG counts words with 3 or more syllables (“polysyllabic”) in a 30-sentence sample, then derives a US grade level. Originally you had to count exactly 30 sentences manually. Today, implementations extrapolate from any sample size.

Where SMOG is used

• CMS patient education materials— required to score at grade 6–8 (SMOG).
• NIH National Cancer Institute— SMOG is the recommended formula for cancer brochures and informed-consent forms.
• Pharmaceutical patient leaflets— many regulatory bodies require SMOG ≤ 8.
• Public health communications— CDC and WHO materials typically score at grade 6–8 by SMOG.

SMOG vs other formulas

All five major readability formulas measure related properties, but SMOG’s specific design makes it more conservative on technical content. Here’s how it compares:

• Vs Flesch-Kincaid: SMOG typically gives a higher grade level by 1–2 points. It penalizes polysyllabic words more aggressively.
• Vs Coleman-Liau: SMOG is syllable-based; Coleman-Liau is character-based. SMOG is more accurate for medical text; Coleman-Liau is more accurate for code-adjacent or technical text.
• Vs Gunning Fog: Both count complex words. Gunning Fog adds sentence length as a second factor. They often agree closely.

Target SMOG scores

• Patient education: ≤ 6 (CMS standard)
• Health communications: ≤ 8 (NIH guideline)
• Consumer health content: ≤ 9
• Medical professional content: 10–12 OK
• Medical journals: 12+ acceptable; readers are specialists

How to lower your SMOG score

SMOG punishes polysyllabic words specifically. To lower the score:

• Replace medical jargon with plain equivalents in patient-facing text. “Hypertension” → “high blood pressure.” “Myocardial infarction” → “heart attack.”
• Reduce nominalizations. “Administration of medication” → “giving the medicine.”
• Use everyday verbs. “Demonstrate” → “show.” “Indicate” → “mean.”