Obtaining precise numbers on the demographics of sexual orientation is difficult for a variety of reasons, including the nature of the research questions. Most of the studies on sexual orientation rely on self-reported data, which may pose challenges to researchers because of the subject matter's sensitivity. Some studies examine self-reported data on same-sex sexual experiences, while other studies examine self-reported identification as homosexual, heterosexual or bisexual. Overall, fewer research subjects identify as homosexual or bisexual, than report having had sexual experiences or attraction to a person of the same sex. Survey type, questions and survey setting may affect the respondents' answers.

A 2016 literature review stated that "Four related phenomena fall under the general rubric of sexual orientation, but they are conceptually and empirically distinguishable. They are listed here not in order of importance but in an order that reflects their degree of historical attention. The first phenomenon, sexual behavior, consists of sexual interactions between persons of the same sex (homosexual), the other sex (heterosexual), or both sexes (bisexual). The second phenomenon, sexual identity, is one's self-conception (sometimes disclosed to others and sometimes not) as a homosexual, bisexual, or heterosexual person. The third phenomenon of sexual orientation is one's degree of sexual attraction to the same sex, both sexes, or the other sex. The fourth phenomenon is one's relative physiological sexual arousal to men versus women (or to male vs. female erotic stimuli), which is more closely related to other aspects of sexual orientation in men than in women." They state that there is no persuasive evidence that the demographics of sexual orientation have varied much across time or place. Bisexuality comes in varying degrees of relative attraction to the same or opposite sex. Men are more likely to be exclusively homosexual than to be equally attracted to both sexes, while the opposite is true for women.

Surveys in Western cultures find, on average, that about 93% of men and 87% of women identify as completely heterosexual, 4% of men and 10% of women as mostly heterosexual, 0.5% of men and 1% of women as evenly bisexual, 0.5% of men and 0.5% of women as mostly homosexual, and 2% of men and 0.5% of women as completely homosexual. An analysis of 67 studies found that the lifetime prevalence of sex between men (regardless of orientation) was 3–5% for East Asia, 6–12% for South and South East Asia, 6–15% for Eastern Europe, and 6–20% for Latin America. The International HIV/AIDS Alliance estimates a worldwide prevalence of men who have sex with men between 3 and 16 percent.

Estimating the demographics of sexual orientation on a global scale is a difficult task, because in many parts of the world discrimination has led people to conceal their sexual identities. Some cross-cultural research has suggested that male homosexuality is more prevalent in stratified societies and may not be a cultural universal, but the empirical findings, conceptual basis, and methodology of such research has been disputed by other cross-cultural researchers.

A small number of people do not feel sexual attraction and identify as asexual, which can be considered a sexual orientation in itself or a lack thereof.

In 2021, Ipsos interviewed people in 27 countries spanning all continents on their sexual orientation and gender identity. For some countries the samples were weighed for representativity, but in others with less internet access, they skewed more urban. In this survey, on average about 80% of people worldwide identified as heterosexual, 3% as gay, lesbian or homosexual, 4% as bisexual, 1% as pansexual or omnisexual, 1% as asexual, 1% as "other", and 11% don't know or won't say. Results indicated that significant differences in sexual identity have emerged between generations across the globe, with the youngest group, or Generation Z, being more likely to identify as bisexual (9%) than Millennials (4%), Generation X (3%) and Boomers (2%). Generation Z and Millennials were also more likely to identify as homosexual, with 4% and 3% doing so respectively, compared to 2% of Generation X and 1% of Boomers. In addition, the survey found that men are more likely than women to identify as homosexual (4% vs. 1%).

The then largest and most thorough survey in Australia was conducted by telephone interview with 19,307 respondents between the ages of 16 and 59 in 2001/2002. The study found that 97.4% of men identified as heterosexual, 1.6% as homosexual and 0.9% as bisexual. For women 97.7% identified as heterosexual, 0.8% as lesbian and 1.4% as bisexual. Nevertheless, 8.6% of men and 15.1% of women reported either feelings of attraction to the same gender or some sexual experience with the same gender. Overall, 8.6% of women and 5.9% of men reported some homosexual experience in their lives; these figures fell to 5.7% and 5.0% respectively when non-genital sexual experience was excluded. Half the men and two thirds of the women who had same-sex sexual experience regarded themselves as heterosexual rather than homosexual.

An update on the above study; it employs the same methodology, has a larger sample (20,055 respondents), and a broader respondent age range (16–69). The study found that 96.5% of the entire sample (or 96.8% of the men and 96.3% of the women) identified as heterosexual, a drop from the 2003 findings (97.5%). Homosexuals accounted for 1.9% of the male population and 1.2% of the female population, a non-significant difference between the sexes. Bisexuals accounted for 1.3% of the male population and 2.2% of the female population. Women were significantly more likely than men to identify as bisexual, and less likely to report exclusively other-sex or same-sex attraction and experience. Similarly, more women reported same-sex experience and same-sex attraction. Nine percent of men and 19% of women had some history of same-sex attraction or experience. More women identified as lesbian or bisexual than in 2001–02. Homosexual/gay identity was more common among men with university education and living in cities, and much less common among men with blue-collar jobs. Both male and female bisexuality were more common among respondents under the age of 20. Male bisexuality was also overrepresented among men in their sixties.