Nuclear magnetic resonance imaging was applied to measure axial velocity, transverse velocity and density profiles within true three-dimensional conical hoppers, fed from a vertical silo. Mass flow and plug flow discharge of a 200-um powder was studied in hoppers of different angles. The density variation along the center axis and velocity profiles are compared to theory for dense compressible granular flow. The velocity profile at the wall boundary, where the shear layer is evident, will also be discussed.