There are a couple of Ki Level Measurment Systems that are use but i will explain the main 3
1. "The Human Scale" - On this scale, a normal person who does not do ki has a energy level of about 200 - 300 and it goes up from there. This scale is not very realistic because it can go up to billions.
2. "DBZ Scale" - This scale is somewhat like the human scale but instead of saying a normal person who does not do ki has a energy level of about 200 - 300 you would say 2 - 3 instead
3 "Darzeth Scale" - This scale is the most realistic out of the previous two shown. The way this works, a normal human who doesnt practice Ki would be around 1-2 as well as any decimal in between. For example, a normal person could be at a level of 1.3. Now this scale, you would be more real. Now keep in mind that this scale CANNOT be converted from any other scale. It is completely different, so you will not be using numbers like 300,000
Now keep in mind that anyone can make up their own scale as well. Pick the one that suits your tastes.