The thicker the tennis string, the longer the lifespan of a tennis string, but with less comfort and power. A thinner tennis string provides you with more ball feeling and control.
Most of the tennis strings have a thickness between 1.20 and 1.40 mm. The relation between tennis string thickness and power, control, lifespan and comfort is described in the table below:
The tennis string thickness is often described in the old measurement 'gauge'. The lower the gauge, the thicker the tennis string and vice versa. An L (which means 'light') is used to describe half gauges. A tennis string with gauge 15L means it is between 15 and 16 gauge. In the table below you can see the corresponding length in millimetres.