Abstract 

  We compute the twist and magnetic helicity of different magnetic flux  ropes derived by theoretical and numerical simulated models. They are provided by the Titov-Demoulin model, magnetohydrodynamic numerical simulations, and the nonlinear force-free field modeling. The boundary of the magnetic flux  rope is determined by the quasi-separatrix layer and the bottom surface. The axis  is determined by the asymmetry property of the magnetic flux rope. Then, we  compute the twist by the Berger-Prior formula that is suitable for arbitrary geometry  and both force-free (the Titov-Demoulin and nonlinear force-free field modeling)  and non-force-free (the magnetohydrodynamic numerical simulations) models. The  magnetic helicity is estimated by the twist multiplied by the square of the axial magnetic flux. We further compare these results with that derived by the finite volume method.