String gauge — the diameter of the string — affects durability, feel, power, and spin in ways that are meaningful for players but rarely explained at the point of sale. Knowing how gauge works gives a stringer a fast, practical lever to adjust a setup without changing string type or tension.
How Gauge Is Measured
String gauge is expressed in millimetres, ranging from approximately 1.10 mm to 1.35 mm for the strings most commonly used. Some manufacturers still reference the older gauge numbering system — 15, 16, 17, 18 — where a higher number means a thinner string. Both systems exist in parallel on packaging and in customer requests.
Common gauge reference points:
- 1.35 mm / 15 gauge — very thick, maximum durability
- 1.30 mm / 15L gauge — thick, durable, less feel
- 1.25 mm / 16 gauge — standard, balanced across most properties
- 1.20 mm / 17 gauge — thinner, more feel and spin, less durable
- 1.15 mm / 18 gauge — very thin, maximum feel and spin, lowest durability
What Thinner Gauge Delivers
A thinner string bites into the ball surface more effectively during contact. The reduced cross-sectional area means more string deflection per unit of ball force, which enhances the snapback effect that generates topspin. This is why spin-focused players tend to prefer thinner gauges within their chosen string type.
Thinner string also moves more freely in the string bed, contributing to feel. The trade-off is durability — less material means the string reaches its failure point sooner.
What Thicker Gauge Delivers
Thicker strings last longer — more material must be worn through before the string fails. For players who break strings often or want to extend time between restrings, increasing gauge is the most direct solution.
Thicker strings also produce a slightly more muted feel. Some players prefer this — it reduces harshness on off-centre hits. Neither is objectively better; it depends on what the player is looking for.
Gauge and String Type Interact
Gauge decisions do not sit in isolation — they interact with string type in ways worth understanding.
Poly at thin gauge: A 1.20 mm poly is significantly livelier than 1.30 mm poly. Players who find full poly too stiff can try dropping a gauge before switching string type entirely.
Multifilament at thin gauge: The durability drop is more pronounced in multifilament than in poly. A thin multi on a hard hitter is a poor combination.
Natural gut gauge: Gut is typically available in a narrower gauge range. The 1.30 mm gauge is standard for most commercial gut.
The Most Common Gauge Requests
In a typical shop, gauge requests fall into predictable patterns:
- "I keep breaking strings" — move to a thicker gauge before changing string type
- "I want more spin" — try dropping a gauge within the current string type first
- "My arm has been sore" — thinner gauge combined with a softer string type reduces stiffness
- "I just want the same as last time" — match the gauge exactly, even if it means checking packaging
For first-time poly players, 1.25 mm is the safe starting point.
Documenting Gauge in the Customer Record
Gauge is a detail that players often do not remember but that makes a real difference to their experience. Recording the gauge alongside the string type and tension in the customer's history means every restring starts from a known baseline rather than a guess.
A player who comes back after six months saying the strings felt great last time can be set up identically — which is the highest compliment a stringer can receive.