  We use magnetoconductance measurements in dual-gated InSb nanowire devices
together with a theoretical analysis of weak antilocalization to accurately
extract spin-orbit strength. In particular, we show that magnetoconductance in
our three-dimensional wires is very different compared to wires in
two-dimensional electron gases. We obtain a large Rashba spin-orbit strength of
$0.5 -1\,\text{eV\r{A}}$ corresponding to a spin-orbit energy of
$0.25-1\,\text{meV}$. These values underline the potential of InSb nanowires in
the study of Majorana fermions in hybrid semiconductor-superconductor devices.
