A: There are a number of factors that determine the tension of the strings and how they feel on a given guitar or bass:
- String gauge
- String materials
- The ratio between string core and wrap
- Scale length
- The break angle of the string at the nut and the bridge
- Amount of neck relief
Our friends at D’Addario have a very useful chart on their site that covers the tensions for a wide array of strings of various types. It’s a big help if you want to maintain the same tension when using alternate tunings, for example.