I understand that the closer to the sound source, the louder the sound. But is there a universal distance sound is measured from the sound source to get consistent measurements?
The sound meter we use specifically states it should be 30cm from the source to be accurate.
It depends on the purpose of the measurement. For large theaters and auditoriums it is going to be specified at the middle of the theater or a little further back. For police enforcing noise ordinances it will be defined by law. For appliance/power tool safety it is going to be less than a meter (3 feet). In general, the distance depends on where the people will be.
As long as you know the air density, and the distance away the object is, you can figure out how much Sound Pressure has dropped by the time it gets to your current meter.