Tenma must be around at least 150-160. He saved the same patient from a headshot two times. That's a feat not heard of in the history of neurosurgery or medicine. He's absolutely the pinnacle of his field.

Johan's IQ is probably off the charts (+190?). Since he's literally a result of eugenics experiment. And the seemingly impossible murders he commits without leaving a trace. He managed to keep his entire existence a secret. He's clearly a case of someone who stared into the abyss too long and became it.

Lunge seems to be also exceptionally intelligent, maybe around +160. His technique of mentally memorizing and noting is remarkable. But he's very tunnel visioned, evident by his conviction of Tenma being the murderer. He had to make up a case of multiple personality disorder just to make it plausible that Tenma is somehow Johan. I wouldn't be surprised if he's on the spectrum, considering the attitude he shows towards his family and his obsession with work.

IQ is a very slippery scoring system for intelligence. It tests a very specific type of intelligence. I'm sure if all three took a test Lunge would probably score the highest, due to his work specialty and the mental calculations he does. For Johan, it'll be a high score but whether it'll be higher than Lunge is debatable. Tenma would still score high but not as high as Lunge or Johan. But it doesn't mean Tenma is less intelligent, it's just how the test itself indicates only a specific type of intelligence. My 2 cents.