Check the SMOG grade level of any text with this free calculator. Paste your writing and see its reading level.
Some writing is hard to read not because the ideas are hard, but because the sentences are long and the words are long. The SMOG readability formula measures exactly that. It gives a grade level: the number of years of schooling a reader needs to understand the text comfortably. A SMOG grade of 11 means the text suits a reader at about United States grade 11 level.
This calculator works out the SMOG grade for any text you paste in. Teachers use it to check school materials. Editors use it to spot writing that needs simplifying. Writers of public information use it to check that ordinary readers can follow their text.
How to use the calculator
- Paste your text into the box.
- Click Calculate SMOG Readability. The tool counts the characters, words, sentences and syllables for you.
- Read the results: the SMOG readability score, the reading level it points to, and a short reading note.
The classic SMOG method works on a sample of 30 sentences. For the most reliable result, paste at least 30 sentences. Shorter texts still produce a score, but the score is less stable, because one long word then has a much bigger effect on the total.
Worked example: 30 sentences with 60 long words
The SMOG formula looks like this:
SMOG grade = 1.0430 × square root of (polysyllables × (30 ÷ sentences)) + 3.1291
A polysyllable is a word with three or more syllables, such as “education” or “government”. Now take a sample with 30 sentences and 60 polysyllables. First, 30 ÷ 30 = 1, so the count stays at 60. Next, the square root of 60 is about 7.75. Multiply by 1.0430 to get 8.08. Finally, add 3.1291 to get 11.21. The SMOG grade is therefore about 11.
In plain terms, that text needs roughly a grade 11 reader. If the same 30 sentences held only 30 polysyllables, the result would be about grade 9. If they held 90 polysyllables, it would be about grade 13. That is the whole idea of SMOG: more long words across the same number of sentences means a higher grade level.
Where a SMOG calculator is useful
- Teachers: checking that a handout matches the class it is written for.
- Editors and writers: finding passages where simpler words would serve the reader better.
- Public information: health, safety and government texts are often aimed at grade 7 or 8, so that most adults can read them.
- Textbook checks: comparing chapters to see whether difficulty rises sensibly through a book.
- Plain language work: measuring a rewrite to prove it really became easier to read.
Honest limitations
SMOG only looks at sentence count and long words. It does not check whether the ideas are clear, whether the order makes sense, or whether the reader knows the subject. A short, clear sentence full of necessary technical terms can score a high grade even though an expert reader finds it easy. A badly organised text can score a low grade and still confuse everyone.
SMOG is also built for English. Its syllable counting does not transfer cleanly to other languages, and its grade levels refer to the United States school system, which does not match other countries exactly. Use it as one signal, next to a human reading of the text, never as the only judgement of quality. Finally, remember the 30-sentence rule: a score from five sentences is a rough hint, not a reliable grade.
Frequently asked questions
What is a good SMOG score?
It depends on the reader. General public information is often aimed at grades 7 to 8. School materials match their class level. Academic and legal writing often scores grades 13 and above, which is fine for specialists but hard for the general public.
How is SMOG different from Flesch reading ease?
Flesch uses average sentence length and average syllables per word to give a 0 to 100 ease score, where higher is easier. SMOG uses only polysyllables and sentence count to give a school grade. They often agree in direction, but they are different scales and should not be mixed.
How many sentences do I need?
Thirty sentences is the standard sample. If your text is shorter, paste all of it and treat the score as an estimate. If it is much longer, the classic method samples 10 sentences from the start, 10 from the middle and 10 from the end.
What counts as a polysyllable?
Any word with three or more syllables. Words like “education”, “population” and “government” count. Short words never count, no matter how uncommon they are.