An incredibly intelligent and skilled geologist, Bert has an IQ of 110.
Penny is clever and resourceful. She has an IQ of around 110 and Sheldon would hate to admit it, but Penny is far from being dumb.
Introduced as Leonard's mother, Beverly is a trained psychologist and author. She has an IQ of 120. Sheldon respects her, thanks to her straightforwardness and logical thinking.
Howard is an engineer and is no doubt a genius. He went to space and studied at one of the best colleges in the world. Howard has an IQ of 140. He also likes building robots for fun.
Howard's wife, Bernadette earns way more than her husband as a scientist. She develops drugs and medications for a big pharmaceutical company. She is one of the smartest people in the group and has an IQ of 160.
With an IQ of 170, Barry is no doubt one of the smartest characters of the Big Bang Theory cast.
A respectful scientist in his field, Leonard has an IQ of 173 and is one of the few characters whose intelligence has been directly mentioned in the show.
Though his IQ is never mentioned directly, Raj is one of the intelligent characters on the show. He is a brilliant astrophysicist and has an IQ of 175.
A neuroscientist by profession, Amy is one of the most accomplished individuals in the show. Though her IQ is never explicitly stated, she probably has an IQ of 180. At the end of the show, she also won a Nobel Prize for her research.
Jim Parson's character Sheldon is indeed one of the most loved characters in the show and his IQ is directly stated. He is truly a genius and he proves it. He has an IQ of 187 and also won a Nobel Prize.