The same relation is given in the following formulae: 'Cd = 5.08*R*(.0563*L/R+.08+.38*SQR(R/L)) 'uufd. DIMENSIONS IN INCHES 'Cd = 2*R*(.0563*L/R+.08+.38*SQR(R/L)) 'uufd. DIMENSIONS IN CENTIMETERS 'WHERE R IS THE RADIUS AND L IS THE LENGTH. "SQR(X)" MEANS THE SQUARE 'ROOT OF X. This, plus Wheeler's approximate inductance formula, has given me very good results in prediction self-resonant frequency of a number of coils I have built here. Ed Phillips