When I worked with a lot of rehab/therapeutic clients (and thus had to fill out a lot of specific charting/goals/treatment results paperwork for insurance and medical team purposes) we tried to be a little more specific with the pain numbers and what they meant, vs using the smiley face thing or just an unguided rate from 1-10.
0 - Absolutely pain free
1-3 Mild Pain - Able to do all activities of daily living with little to no modifications needed.
1- pain is present off and on but barely noticeable and often forgotten about.
2 - minor pain is annoying and definitely present most of the time with occasional stronger twinges.
3 - pain is annoying and distracting, but you can adapt and get used to it, still performing your usual activities without moderation.
4-6 Moderate Pain - interferes significantly with daily life activities
4 - moderate pain. You can be distracted from it if you are very engaged in something else, but only for a certain period of time, and you are starting to need to modify your daily activities because you can't function fully.
5 - moderately strong pain. You cannot ignore it for longer than a few minutes. You can push through to so many or your daily activities or social activities, but you must limit both significantly.
6 - moderately strong pain that significantly impacts your daily activities and cannot be ignored or distracted from at all. This level of pain impacts your ability to speak normally/carry on an undistracted conversation.
7-10 Severe pain - Disabling/cannot perform functions of daily living
7 - the pain interferes or severely limits your ability to sleep. It is severe pain that dominates your senses and significantly limits your ability to perform daily tasks or keep up with social endeavors.
8 - intense, acute pain. Severely limits any/all physical activities. Conversation with others is extremely difficult
9 - excruciating pain. Involuntary crying out/vocalizations. Unable to coherently converse with others.
10 - unspeakable pain, delirious, bedridden, unable to perform any tasks or communicate with people.
Unmedicated childbith pain is usually described as a 7-8 level, for reference. If you're at a 9-10 you're in the hospital.
Pain scale is not really talking about pain alone, it's pain and /function/. If you are at the doctors office talking with them coherently during your appointment, having walked there under your own power you are not at a 9 or 10 on the pain scale even if it is indeed the worst pain you personally have experienced.