  We present a calculation of the wavevector-dependent subband level splitting
from spin-orbit coupling in Si/SiGe quantum wells. We first use the
effective-mass approach, where the splittings are parameterized by separating
contributions from the Rashba and Dresselhaus terms. We then determine the
parameters by fitting tight-binding numerical results obtained using the
quantitative nanoelectronic modeling tool, NEMO-3D. We describe the relevant
parameters as a function of applied electric field and well width in our
numerical simulations. For a silicon membrane, we find the bulk Rashba
parameter to be linear in field, $\alpha = \alpha^1E_z$ with $\alpha^1 \simeq
2\times$ 10 $^{-5}$nm$^{-2}$. The dominant contribution to the spin-orbit
splitting is from Dresselhaus-type terms, and the magnitude for a typical flat
SiGe/Si/SiGe quantum well can be as high as 1$\mu$eV.
