It's your baseline, so if they try some treatment and your pain is still not changing then they know they should continue making adjustments

There is a blood test for this fyi. Some protein or something can indicate the pain you have. I forgot their name but I know the research and medics of it. But I don't care to tell you that.

Other people had good answers to this question, like Sean, Arthur and Kate.

Childbirth for me = taking the biggest constapoo in the world. While having diarrhea pain pangs. I’d rate it 8. Getting hit on the nose or stubbing your toe … now those are 10s in my book.

Since it is your personal and individual scale of pain the doctor knows how much pain it is for you. That is important because not his scale is important to predict when you cannot bear it any longer. In terms of diagnosis it is also helpful to know if you are the type for feeling pain early or not. it is not about absolute accuracy but about the level of pain load you can or cannot bear. When a patient faints due to pain it isn't of importance that you would sense the same pain level as nothing. As a doc you will want to prevent a fainting person to hit the floor with the head, you know?

I tend to go 1-5 if I can actually say a number without saying something like 'GFFFOOOOFFFTTTTTTTTTTT.......FUUUUUCCCCKKKKKK'. If I do say that then its going to be in the top half, especially if I swear.

. I can rate my pain pretty accurately. If I can’t stand up or am writhing or crying then that’s probably a 9.

Yes, it's impossible to objectify pain, it's always going to be subjective and relative - my 7 does not equal your 7 and wasn't meant to be treated as such, it's just used to establish an individual's baseline to compare to that same person the next hour or day or whatever

I always say 11

Doctors usually make a number of assumptions given a common set of patient characteristics. In that way, they're able to translate our relative rating to their more absolute scale.