I managed to find this for you:

" ...
This gives us the equation:

SW = ((Lc*(H + S/2) - 14*(H + S) - 10G) / 50) - 124

Whe
SW = Swingweight with respect to D-0.
That is: if SW = 2, then swingweight is D-2.
if SW = -4, then swingweight is C-6.
Lc = nominal club Length (inches)
H = Head weight (grams)
S = trimmed Shaft weight (grams)
G = Grip weight (grams)

Just a few more qualifications and caveats about this equation before I

give it a rest:

To use the formula, you have to compute a trimmed length from the
shaft's raw length and raw weight (which are in most catalogs). I
usually make the simplifying assumption that it's proportional to the
trimmed length. That is:

S = raw shaft weight * (cut shaft length/raw shaft length)

Historically, this has been a decent approximation for most shafts.
However, it doesn't accommodate tip-heavy shafts, which to be accurate
must be computed by separately considering the tip-trimming and the
butt-trimming.

Ed Stephenson
.... "

As I don't play golf, it doesn't mean much to me, but it might to you.

Hope this helps.

Pete

Clubmaker wrote:
I have heard that the Excel formula exists and requires the trimmed shaft
weight (in grams), shaft length (in inches), weight of the head (in grams),
the grip weight (in grams), and the fulcrum point from butt end of the grip
(14 inches) of the finished club to produce an accurate swing weight value
forthe club. It gives the swing weight prior to full assembly which is
really the best time to make adjustments.

Thanks,
CWR