Swingweight (SW, swing weight, swinging weight) is one of attempts to quantify the heft or headweight feel of a golf club. It specifies how heavy the club feels to a golfer swinging it.
In accordance with the principles of physics, club sets should be matched basing on moment of inertia (MOI) of the clubs about their butts. But in the past golfers needed any simple method and the value of swingweight was easy to estimate. Nevertheless the swingweight fitting is not a bad match at all. Therefore many golfers still traditionally use it as the simplest method of matching club set.
In fact, no “swingweight” exists in the swing physics. It is only an arbitrary expression of the weight distribution of a golf club. Swingweight is measured as the amount of torque the weight of the club exerted about a pivoting fulcrum point.
In golf history, clubfitters have used two different Swingweight scales: “Lorythmic” (the most popular nowadays) and “Official” (used in vintage scales).
Swingweight in Lorythmic scale
Lorythmic (Lorythm) scale uses the fulcrum point at 14” from the butt. The lorythmic scale expresses the swingweight value in alphanumeric symbols (letter + number). The scale uses the letters A, B, C, D, E, F and G, and the digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9. The lower the letter and digit, the less the headweight the golfer notices when the club is swung. So the symbol A0 indicates the lightest heft, progressing up to the heaviest, G9. The gap between adjacent combinations of letter and number is known as a “swingweight point”. Usually manufacturers take the standard for men’s clubs from D0 to D2, and for women’s clubs from C5 to C7.
Swingweight in Official scale
Official scale is based on the fulcrum point at 12” from the butt. Swingweight on this scale is traditionally expressed in “ounces”. Alternatively, some use the moment of force units such as “inch-ounces” (in*oz). The Official Swingweight expressed in ounces indicates the load that has to be applied at the grip end (butt) to balance the golf club. The manufacturers take the standard for men’s clubs from 20.0 do 20.5 ounces (240 to 245 in*oz). Accordingly for women’s clubs it is 19.1 do 19.5 ounces (230 to 235 in*oz). On Official scale the gap of 0.2 ounce (or 2 inch-ounces) corresponds to one “swingweight point” on Lorythmic scale.
Sometimes swingweight is expressed in units of force that must be applied to the butt of the club to maintain the balance of the club supported at the fulcrum point. Naturally, in the Lorythmic scale, this point is located 14 inches from the edge of the grip, while in the Official scale it is 12 inches. Then, the most frequently used unit of force is newton (SI unit).
Generally most golfers feel the difference of three swingweight points to be quite noticeable. Some golfers can feel a difference of two points, but the difference in feel is subtle. Consequently, very few golfers can feel a difference of one swingweight point (or 0.2 ounces on the Official scale, respectively).
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update: October 2021