The poll, released on Wednesday, also found that 86.7% of Americans identify as heterosexual or straight and 7.6% didn't answer the question about their sexual orientation.
The increase in the percentage of Americans identifying as LGBTQ+ was expected, according to Gallup, as the percentage increased on average by 0.3 points per year in 2016 and 2017 – meaning that, if the trend continued since then, the total increase would have been about one percentage point.
Over half of LGBTQ+ adults who responded to the survey identify as bisexual, while a quarter say they're gay, 11.7% say they're lesbian and 11.3% say they're transgender. Another 3.3% indicate another non-heterosexual preference or term to describe their sexual orientation.
In total, 3.1% of Americans identify as bisexual, 1.4% as gay, 0.7% as lesbian and 0.6% as transgender, according to the poll.
The percentage of Americans who identify as LGBTQ+ increased amid the younger generations, with one in six adult members of Generation Z identifying as LGBTQ+, while less than 2% of Americans born before 1965 identified as something other than heterosexual.
Some 72% of Gen Z adults who identify as LGBTQ+ stated that they are bisexual, meaning that 11.5% of Gen Z adults in the US say they're bisexual. In comparison, about half of all LGBTQ+ millennials stated that they are bisexual. In older groups, the split of identifications is about equal.
The poll additionally found that women are more likely than men to identify as LGBTQ+ and are more likely to identify as bisexual. More liberals and moderates identified as LGBTQ+ than conservatives, with 13% of liberals, 4.4% of moderates and 2.3% of conservatives identifying as LGBTQ+.
The Gallup poll is based on over 15,000 interviews conducted throughout 2020 with Americans aged 18 and older. Respondents were able to provide more than one response, which resulted in totals exceeding 100%.