I keep seeing people online claim Einstein had an IQ of 160 or 180 or whatever number they feel like throwing out. But I also know that IQ tests were barely developed during his lifetime and I have never seen anyone cite an actual source for these numbers. Did Einstein ever take a standardized IQ test and if not where do these scores come from and how seriously should we take them?
Einstein almost certainly never took a modern IQ test and any specific number you see attached to his name is essentially made up 
IQ testing was in its infancy during his lifetime and there is no documented record of him ever sitting a standardized cognitive assessment. The scores that get circulated, usually somewhere between 160 and 180 depending on who is making the claim, are retrospective estimates based on biographical information and achievements. These are called historiometric estimates and while they are an interesting exercise they carry enormous uncertainty. The error bars on any posthumous IQ estimate are so wide they render the specific number basically meaningless. What we can say with reasonable confidence is that Einstein showed exceptional spatial reasoning, strong mathematical intuition, and unusual capacity for abstract thought, all of which are g loaded abilities. But translating that into a precise IQ score is not science, it is speculation dressed up as a number 
The irony is that Einstein himself was reportedly a late talker and performed unevenly in school 
If he had taken a childhood IQ test he might not have scored as dramatically as the mythology suggests. Genius at the highest level often looks weird and uneven up close.