Some 20% of Titan's surface is covered in large linear dunes that resemble in morphology, size and spacing (1–3 km) those seen on Earth. Although gravity, atmospheric density and sand composition are very different on these two worlds, this coincident size scale suggests that the controlling parameter limiting the growth of giant dunes, namely the boundary layer thickness [Andreotti et al., 2009). Nature, 457, 1120–1123], is similar. We show that a ~3 km boundary layer thickness is supported by Huygens descent data and is consistent with results from Global Circulation Models taking the distinctive thermal inertia and albedo of the dune sands into account. While the boundary layer thickness on Earth controlling dunes can vary by an order of magnitude depending on the proximity of oceans, which have very different thermal properties from dry land, the relative invariance of dune spacing on Titan is consistent with relatively uniform thermal properties near the dunes and no prominent variation with latitude is seen.