Gauges Explained

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Gauge is the thickness of the string. The confusing part is that the number runs backwards: a higher gauge number means a thinner string.

What you gain and what you give up

Thicker (lower number)

  • Lasts longer before it breaks.
  • Holds tension a little better.
  • Firmer, more muted response.
  • A touch less spin and less feel.

Thinner (higher number)

  • More elastic, so more power and more feel.
  • Most players get a little more spin.
  • Softer on the arm at the same tension.
  • Breaks sooner — sometimes much sooner.
There is no better gauge, only a trade between how long the string lasts and how it feels. Almost everyone is choosing between 16 and 17.

Which one should you use?

  • You break strings every week or two. Go thicker. 16 in a polyester, or 15L if you are in a multifilament and still sawing through it.
  • You almost never break strings. Go thinner. 17 will give you more feel and more spin for no practical cost, and 18 if you want to go further.
  • Your arm is complaining. Thinner helps, because a thinner string of the same material is more elastic. Changing material helps more — see string materials.
  • You have no idea. 16 if you hit hard, 17 if you don't. You can change one thing at a time from there.

The number runs backwards

15 is the thickest string in common use and 19 the thinnest. An L after the number stands for "light", meaning a little thinner than the plain number but not as thin as the next one up — so 16L sits between 16 and 17.

Thickest to thinnest, the full order is:

1515L1616L171819

What the difference actually looks like

ROUND — DIAMETERHEX POLY — ACROSS THE FLATSØ1.3515LVelvetØ1.3016most stringsØ1.2517most strings1.2816LHex Poly1.2317Hex Poly1.1818Hex PolyDimensions in mm. Enlarged, true to scale against each other.

Every gauge Golden Set makes, at Golden Set’s own measured diameters. The gap between the thickest and the thinnest is under two tenths of a millimetre — small on paper, clearly felt on court.

Gauge in millimetres

Each gauge designation covers a range rather than a single figure, and brands sit at different points within it. Here is where Golden Set sits.

Gauge Golden Set Usual range Strings
15L 1.35 mm 1.33 – 1.41 mm Velvet
16 1.30 mm 1.26 – 1.34 mm Snake-Bite, Snake-Bite Smooth, Power Cord, Synthetic Gut, Satin, Velvet
16L 1.28 mm * 1.22 – 1.30 mm Hex Poly
17 1.25 mm 1.16 – 1.24 mm Snake-Bite, Snake-Bite Smooth, Power Cord, Synthetic Gut, Satin, Velvet
17 1.23 mm * 1.16 – 1.24 mm Hex Poly
18 1.18 mm * 1.06 – 1.16 mm Hex Poly

* Hex Poly is measured across the flats — see below. Ranges follow the usual industry convention; charts vary between sources, particularly at the thin end. You will also see 17L on some brands; it sits between 17 and 18 and is not defined consistently.

Why the Hex Poly numbers look small

A hexagonal string does not have one diameter. Measured across the flats — the narrowest way across — Hex Poly 17 reads 1.23 mm; measured corner to corner it is noticeably wider. Golden Set quotes the across-the-flats figure, which is the conservative one.

Hex Poly is also run deliberately a little thinner than the round strings at the same designation. Between the two, its numbers are not directly comparable with a round string’s diameter — which is why the diagram above draws it as a hexagon rather than a circle.

Gauge and tension go together

A thinner string stretches more at the same tension, so dropping a gauge makes the whole bed feel softer and livelier. If you move from 16 to 17 and the racquet suddenly feels too powerful, add a pound or two rather than going back up a gauge.

More on that on the tension page.

Gauge in a hybrid

In a hybrid the two strings do not have to match. The usual guidance is to keep the crosses the same gauge as the mains or thicker — a thinner cross has a sharper bend where it passes over the mains, which concentrates the pressure and wears them out faster.

The exception is the all-polyester hybrid, where a thinner cross adds spin and elasticity at a known cost in durability. The hybrid guide goes through each combination.

What Golden Set makes

String Type Gauges Reel
Snake-Bite Shaped co-polyester 16 (1.30) · 17 (1.25) 660 ft
Snake-Bite Smooth Round co-polyester 16 (1.30) · 17 (1.25) 660 ft
Hex Poly Hexagonal co-polyester 16L (1.28) · 17 (1.23) · 18 (1.18) * 660 ft
Power Cord Soft co-polyester 16 (1.30) · 17 (1.25) 660 ft
Synthetic Gut Solid core with a wrap 16 (1.30) · 17 (1.25) 660 ft
Satin Multifilament 16 (1.30) · 17 (1.25) 360 ft
Velvet Multifilament 15L (1.35) · 16 (1.30) · 17 (1.25) 360 ft

Diameters in millimetres. * Hex Poly measured across the flats. Hex Poly 18 is the thinnest string we make; Velvet 15L the thickest.

Shop all tennis strings → Hybrid & blending guide →

Related: Tension explained · Hybrid & blending guide · String materials & construction

Golden Set strings are sold in bulk reels — a 660 ft reel restrings roughly 16 racquets, a 360 ft reel roughly 9. Updated September 2026.