String gauge is simply the diameter of the string, measured in millimetres. In tennis, you’ll commonly see gauges from around 1.15 mm to 1.35 mm.
The rule is simple: the lower the number, the thinner the string. So a 1.20 mm string is thinner than a 1.30 mm string.
You may also see US gauge numbers such as 16, 16L, and 17. These work in the opposite direction — a higher gauge number means a thinner string.
Changing gauge can noticeably change how a stringbed feels and performs. The trade-off is usually between spin and feel on one side, and durability and stability on the other.
Thinner strings: 1.15–1.24 mm
A thinner string generally gives you a livelier and more responsive stringbed.
- More spin potential — thinner strings can move and snap back more easily, particularly in spin-friendly co-polys.
- More feel — the stringbed can feel more responsive and give you better feedback on touch shots.
- More power — thinner strings generally deform more at impact, which can create a livelier response.
- Less durability — the main trade-off. A heavy hitter can break a thin string significantly faster than the same string in a thicker gauge.
Thinner gauges are particularly interesting for players who rarely break strings and want to maximise spin, feel, and responsiveness.
Thicker strings: 1.28–1.35 mm
A thicker string generally produces a firmer and more durable stringbed.
- More durability — the main reason players choose a thicker gauge.
- More stability — the stringbed tends to feel firmer and more solid at impact.
- A more controlled response — particularly useful for players who generate plenty of power themselves.
- Slightly less spin and power potential — compared with the same string in a thinner gauge.
The difference isn’t enormous, but over a full match or several weeks of play, the change can be noticeable.
How to choose your gauge
The easiest place to start is how often you break strings.
You break strings very often
Try 1.30 mm or thicker. If you’re breaking a set every few sessions, going thinner for extra spin may simply mean restringing more often. A thicker version of the same string can give you a much longer playing life while keeping the characteristics you like.
You break strings every few weeks
1.25 mm is a good starting point. It’s the most common middle-ground gauge for co-poly and offers a balanced combination of spin, control, feel, and durability.
You rarely or never break strings
You can experiment with 1.20 mm or thinner. You’ll generally get a livelier response, more feel, and potentially more spin — and because durability isn’t a major concern, you can prioritise performance instead.
One simple rule
If you love a string but keep breaking it, try the same string in a thicker gauge before changing strings completely. It’s often the easiest way to increase durability without losing the characteristics you liked in the first place.