Intelligence is the capacity to acquire and apply knowledge. Some feel IQ (Intelligence Quotient) tests can measure Intelligence. Many, if not the majority disagree with this. So there is no widely accepted form of measuring intelligence. IQ 100xMental Age / Chronological Age, is the closest you can get to measuring intelligence.
However IQ tests require you to have certain knowledge in subjects and to apply that knowledge. True application of intelligence would be to study questions of exact types and apply that knowledge.
IQ tests assume you have certain knowledge and are ready to use it. Some people simply have bad attention to detail or aren't good at taking tests.
In my opinion, there is no generalized and extremely accurate way to measure Intelligence. There is a crude, and sometimes fairly accurate method in the way of an IQ test. I'm currently doing a project on IQ amongst other Psychology related issues. I could go on and on if you want more information. My post was somewhat based on opinion so many might disagree with my conclusion.