SMOG Index Calculator

• SMOG = 1.0430 × √(polysyllables × 30 ÷ sentences) + 3.1291
• Calibrated for FULL comprehension — scores run 1–2 grades above Flesch-Kincaid by design
• The standard in healthcare; patient materials typically target SMOG grade 6–8
• Statistically valid on 30+ sentences — short samples inflate the error bars
• Only counts polysyllabic words (3+ syllables) — sentence length enters via the ratio

Frequently Asked Questions

Why is my SMOG score higher than my Flesch-Kincaid grade?

By design. SMOG was calibrated against 100% comprehension, versus partial-comprehension criteria for other formulas — so it consistently reads 1–2 grades higher on identical text. Neither is wrong; they answer different questions ('can readers follow it?' vs 'will readers fully understand it?').

What SMOG grade should patient materials target?

Grade 6–8 is the widely cited range for consumer health content, with 6 as the gold standard for universal materials. Most published patient-education content scores well above this, which is exactly the problem SMOG scoring is meant to catch.

Is SMOG accurate on short texts?

The formula is designed for 30+ sentence samples; on shorter texts the score still computes but with wide error bars — a single polysyllabic word can move a short sample noticeably. For paragraphs, treat it as directional and confirm on the full document.

What does SMOG stand for?

Simple Measure of Gobbledygook — McLaughlin's deliberate nod to fog-index tradition and to the smog of unreadable prose it measures. The whimsical name predates its adoption as healthcare's most conservative readability standard.

Is my text uploaded anywhere?

No — the analysis runs entirely in your browser. Nothing you paste is sent to a server, stored, or logged, which makes the tool safe for unpublished drafts and confidential documents.