The SMOG formula is widely used to determine how easy written health education materials are to read and comprehend. This study was conducted to assess whether the SMOG formula, originally developed and tested in English, was also valid for texts written in Spanish and French. Readability scores from a sample of passages written in Spanish, English, and French were analyzed. Study results showed that the SMOG formula seemed to be consistent in measuring readability in the three languages. However, SMOG scores varied from language to language. Two hypotheses are being laid out to explain these results. First, the SMOG equation is systematically biased for texts in Spanish or French. Second, English is more readable than French, and French is more readable than Spanish. Under the assumption of a systematic bias in the SMOG formula, the so-called SOL formulas are presented here to convert SMOG scores between Spanish, English, and French. In addition, a new scale for grading reading difficulty is proposed based on SMOG scores obtained from classical literature. This is important to the extent that it will provide Spanish speaking and French speaking health communicators with a readability formula for preparing written materials appropriate to the level of comprehension of specific target audiences.