Before revision:  For A-DNA it is approximately 28 deg., and for B-DNA  approximately 38 deg., in accord with the principle of optimal packing of tubular double helices .
After revision:  For A-DNA it is approximately 28 deg., and for B-DNA based on differential geometry is compared with numbers obtained from existing empirical data. The crystallographic studies shows that the pitch angle is approximately 38 deg., in accord with the principle of optimal packing of tubular double helices .