2 October 2026 · 9 min read
Conforming club and ball: length, head size, CT value and weight under the R&A Rules
48 inches of length, 460 cm³ of head volume, 257 microseconds of CT and 45.93 g for the ball: the R&A limits, how to spot breaches and where the list is.
A club may be no longer than 48 inches (1.219 m), a putter excepted. A driver head may be no bigger than 460 cm³ plus a 10 cm³ tolerance, and the characteristic time (CT) of its face may not exceed 239 microseconds plus an 18 tolerance (R&A, Equipment Rules Part 2). A ball may weigh no more than 45.93 g and must measure at least 42.67 mm (R&A, Part 4), and anyone who strikes with a non-conforming club in a round under the Rules of Golf is disqualified (R&A, Rule 4).
The limits for the club
The R&A Equipment Rules set limits for every part of the club. The table gives the figures that matter most when you buy, in inches and in millimetres.
| Feature | Limit | Applies to |
|---|---|---|
| Length | at least 18 inches (0.457 m), at most 48 inches (1.219 m) | all clubs, a putter may be longer |
| Head volume | at most 460 cm³ (28.06 cubic inches), plus a 10 cm³ (0.61 cubic inch) tolerance | woods |
| Head width | from heel to toe at most 5 inches (127 mm) | woods |
| Head height | from sole to crown at most 2.8 inches (71.12 mm) | woods |
| Moment of inertia | at most 5,900 g cm², plus a 100 g cm² tolerance | woods |
| Characteristic time (CT) | at most 239 microseconds, plus an 18 tolerance, so 257 | drivers and other clubs up to 35 degrees of loft, except putters |
| Grip cross-section | at most 1.75 inches (44.45 mm) in any direction | all grips, circular except on putters |
| Groove width and depth | width at most 0.035 inches (0.9 mm), depth at most 0.020 inches (0.508 mm) | clubs with grooves in the impact area |
| Putter head | from heel to toe at most 7 inches (177.8 mm), from sole to top at most 2.5 inches (63.5 mm) | putters |
For woods and irons, length is measured with the club on a horizontal plane, the sole set against a plane of 60 degrees, and the length runs from the point where the planes meet to the top of the grip. Part 2 names no weight limit for the club, which I checked in the text on 2 October 2026. Weight only comes in through the moment of inertia: if you stick lead tape on a driver, you must be sure the club stays under the limit. With a proven medical need the Committee may allow longer clubs, which Golf with a disability explains. Which loft suits your speed is shown in Which driver loft suits you.
The CT value: what it measures and where the limit is
CT stands for characteristic time. PGA Deutschland calls it a measure of the impact efficiency of a driver face, sometimes also the “spring effect” (PGA Deutschland, teaching manual). A higher CT impact efficiency transfers energy to the ball more efficiently, which on paper means more distance. For the trampoline effect (COR) the R&A has set a maximum of 0.83. Because the COR value can only be determined in a very complicated way, the R&A and USGA agreed on the CT test.
The limit is 239 microseconds plus a test tolerance of 18, which gives a maximum of 257. According to an R&A notice of 21 January 2016, clubs with more than 35 degrees of loft are deemed to conform and are not tested. It checks the rest, except putters, with a pendulum tester: if the CT value in the impact area is above 239 plus 18 microseconds, the club does not conform. For flat iron heads a further test comes first in that case (R&A, Spring Effect and Dynamic Properties). So the CT test concerns drivers, woods, hybrids and irons up to 35 degrees of loft.
You cannot see the CT value and can hardly measure it without special equipment. The R&A writes that the spring effect can hardly be measured without special equipment and cannot be judged from the outside. That is why the list of permitted driver heads exists, see below.
The ball: weight, diameter and what else is tested
| Feature | Limit |
|---|---|
| Weight | at most 45.93 g (1.620 ounces), there is no minimum weight |
| Diameter | at least 42.67 mm (1.680 inches), there is no maximum |
| Symmetry | The ball must not have properties that differ from those of a symmetrical sphere. |
| Initial velocity and overall distance | The limits are set in test standards of the R&A and the USGA, not in the text of the Rules. |
A ball with a diameter of 1.62 inches was once in circulation and has been prohibited worldwide since 1990 (R&A, Equipment Rules Part 3). Which ball suits your speed is covered in Which golf ball suits me.
How to spot a non-conforming club
- Length: A club other than the putter is longer than 48 inches.
- Volume marking: The head carries a cc figure above 460. The R&A rules such a club non-conforming, whatever the real volume is.
- Grip: It is not round (except on a putter) or has hollows that fingers fit into. Then it counts as “moulded for the hands”.
- Two striking faces: One is allowed, a putter may have two identical ones opposite each other.
- Adjustment without a tool: If a weight can be adjusted with a coin, the club does not conform. Every possible setting must also conform to the Rules.
- Spring-effect advertising: If the maker says the club is over the limit, it counts as non-conforming.
A sticker on the face counts as a non-permissible attachment, but it can be removed: if you take it off before the stroke, there is no penalty (Rule 4.1a).
The R&A list: how to look up a driver and a ball
The List of Conforming Driver Heads lists the models and lofts of all driver heads that the R&A or USGA has tested and found conforming. It is updated every Monday morning and can be searched online in the Equipment Search. Every model is a separate entry with its lofts and identification markings. Identical markings on the sole are not enough to identify the model.
If your driver is not on it, there can be three reasons: it was never submitted, it is non-conforming, or it dates from before 1999. Then ask the maker or the R&A. The R&A recommends the list as a condition of competition only for events with highly skilled players. Balls are similar: the List of Conforming Golf Balls is updated monthly, a model stays on it for a year, and the R&A needs 24 samples for a test. Normally only events with expert players introduce a requirement to play a ball from the list. Otherwise a ball is assumed to conform unless there is strong evidence to the contrary.
What this means for you
Before you buy a driver, check three things:
- Is the driver model with your loft on the R&A list?
- Is the length at most 48 inches, and does the head carry no cc figure above 460?
- Is the grip round, and can nothing be adjusted without a tool?
A stroke with a non-conforming club or ball costs disqualification (Rules 4.1a and 4.2a). Merely carrying it is penalty-free, but it counts towards the 14 clubs allowed, as Golf bag and trolley shows. A club that conformed when new stays conforming when normal use wears it. That helps when you buy second-hand, which Used clubs and lake balls describes. If you are only starting with a first set, Golf beginner set: which clubs covers the choice.
What a fitting measures and costs is in Golf fitting in Switzerland. Afterwards you look up the head you are buying in the list.
Test heads and find a venue
Which clubs you can try in the bay you clarify with the venue beforehand. 81 of the 110 indoor venues offer coaching (as of 2 October 2026), and they are listed under indoor golf training. The map shows all venues by canton, and if you are new, start with golf simulator for beginners.
Frequently asked questions
How long and how big may a driver be?
The club may be no longer than 48 inches (1.219 m), a putter excepted. The head may have a volume of at most 460 cm³ plus a 10 cm³ tolerance, and measure at most 5 inches (127 mm) from heel to toe and at most 2.8 inches (71.12 mm) from sole to crown (R&A Equipment Rules, Part 2).
What is the CT value on a driver, and what is the limit?
CT is the characteristic time of the face, a measure of the spring effect. The limit is 239 microseconds plus an 18 microsecond test tolerance, so 257 at most. The R&A tests clubs up to 35 degrees of loft, except putters, and does not test above that. You cannot see the value, which is why the list exists.
How heavy and how big may a golf ball be?
A golf ball may weigh at most 45.93 g (1.620 ounces) and must have a diameter of at least 42.67 mm (1.680 inches). There is neither a minimum weight nor a maximum size. Initial velocity and overall distance are limited in test standards of the R&A and USGA (R&A Equipment Rules, Part 4).
Where do I check whether my driver is on the conforming list?
In the R&A's List of Conforming Driver Heads, which is updated every Monday morning and can be searched online in the Equipment Search. Look at model, loft and identification markings. If it is not there, it was never submitted, is non-conforming or dates from before 1999.
What happens if I play with a non-conforming club?
A stroke with a non-conforming club costs disqualification (Rule 4.1a). Merely carrying it in the bag is penalty-free, but it counts towards the 14 clubs allowed. The responsibility for the clubs conforming lies with the player.
Sources
- R&A: Ausrüstungsregeln, Teil 2, Konformität der Schläger (Länge, Kopfmasse, Volumen, Trägheitsmoment, Griff, Rillen, Federeffekt)
- R&A: Ausrüstungsregeln, Teil 3, Spielregeln für den Golfball (Liste der regelkonformen Bälle, Mustern, Modell-Platzregel)
- R&A: Ausrüstungsregeln, Teil 4, Konformität der Bälle (Gewicht, Durchmesser, Symmetrie, Prüfnormen)
- R&A: Regel 4, Ausrüstung des Spielers (regelkonforme Schläger und Bälle, Disqualifikation, Verschleiss)
- R&A: Spring Effect and Dynamic Properties (CT-Grenze 239 plus 18 Mikrosekunden, Prüfung bis 35 Grad Loft)
- R&A: List of Conforming Driver Heads (wöchentliche Liste, Equipment Search, Gründe für fehlende Einträge)
- PGA Deutschland: Lernunterlage Golftechnik (März 2019) (Rückprallzeit CT, COR 0,83)
- Swiss Golf Simulators: eigene Einträge (Indoor-Anlagen mit Coaching, Stand 2. Oktober 2026)