The most popular way of determining one's intelligence is with an Intelligence Quotient (better known as I.Q.) test. Two among the most influential psychologists studying intelligence, Lewis M. Terman and Leta Hollingworth, suggested two different numbers when considering the cut-off for genius in psychometric terms. Dr. Terman considered it to be an IQ of 140, while Dr. Hollingworth put it at an IQ of 180. Moreover, both these numbers are ratio IQs, which in deviation values used presently put the genius IQ cut-off at 136 (98.77th percentile) and 162 (99.994th percentile) respectively. There are also several examples of people with IQ levels in the genius range who have a disability or very low level in one of the subcategories. In addition to the fundamental criticism that intelligence measured in this way is an example of reification and ranking fallacies, the IQ test has also been criticized as having a "cultural bias" in its interpretation despite claims that these tests are designed to eliminate race/gender for example by predicting numerical sequences, etc. Accordingly, the definition of genius embraces those who do not necessarily have an IQ test score of this stature, or who have not even taken such a test. A vast intelligence is needed, but the mental state of possessing genius is based primarily upon an incredible understanding of complex issues and problems, and a profound creativity and imagination.

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