Abstract The permeability of lunar soil simulant, JSC-1A, is measured over a range of bulk densities from 1550 to 2000 kg m−3. The corresponding viscous flow permeability is 1 × 10−12 m2 to 6.1 × 10−12 m2 for this bulk density range. Implications of these values on the contamination of regolith by rockets, on barrier/enhancement to bulk flow of ice, and on cratering are discussed. Although the particle size and shape distribution of the JSC-1A are extremely wide, the permeability measurements agree surprisingly well with the Carman–Kozeny equation. The results provide evidence that the Carman–Kozeny model could be applicable to other naturally occurring soils if effective soil properties are considered.