вот такой документик у меня обнаружился звиняйте что по аглицки :o)

FIS calculates Radius:
Formula used for Radius calculation R

with L= (L1-20%) + (L2-10%) or L= 0,8 x L1 + 0,9 x L2

L1 = Distance from the tip to the point of minimum ski width
L2 = Distance from the tail to the point of minimum ski width

Radius = (L*L)/(2000 x (S + H - 2 x W))

S = max width at the tip
H = max width at the tail

Both measured at the running surface

Important: W is measured at the minimum ski width location

Measurement Procedure:
1. Measurement of W, narrowest width of the ski (or minimum width at the ski middle area)
2. Measurement of L1, front lenght, and L2 back length, from the W location
3. Calculation of L1-20% and reading of its location , measurement of S
4. Calculation of L2-10% and reading of its location, measurement of H
5. Calculation of, the ski radius

Example:
S = 108
W = 63 L1+L2 = 1730
H = 99
L1 = 990L1-20%= 792
L2 = 740 L2-10%= 666
L = 1458

R = 13.122

This was copied from the FIS excel spreadsheet for the FIS rules for Season 2000/2001 and 2000/2002.