Is there any measure which determines the level of impurity?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

In principle all things are pure, and we cannot rule that something is impure except with evidence from the Book of Allaah and the Sunnah of the Prophet or with a consensus of all Muslim scholars from the Salaf. For instance there is evidence that urine, excrements, pre-seminal fluid [Mathiy], menses, dead meat, the pig's blood, the dog's saliva, and the dung of a donkey are impure. According to the majority of scholars intoxicants are also impure. All these details are detailed in the books of Fiqh (Islamic jurisprudence).

In some cases, some impurities could be overlooked like a small amount of blood. Anyway, a person should avoid whispers, as there is evil and harm in them, and he should not rule that something is impure unless he has evidence as already discussed.

Allaah Knows best.