diff --git a/common/Domain.cpp b/common/Domain.cpp
index 931ac5dd..f7427e0c 100644
--- a/common/Domain.cpp
+++ b/common/Domain.cpp
@@ -545,7 +545,6 @@ void Domain::ReadIDs(){
 
 	// Compute the porosity
 	double sum;
-	double porosity;
 	double sum_local=0.0;
 	double iVol_global = 1.0/(1.0*(Nx-2)*(Ny-2)*(Nz-2)*nprocs);
 	if (BoundaryCondition > 0) iVol_global = 1.0/(1.0*(Nx-2)*nprocx()*(Ny-2)*nprocy()*((Nz-2)*nprocz()-6));
diff --git a/common/Domain.h b/common/Domain.h
index 038627c2..e298836c 100755
--- a/common/Domain.h
+++ b/common/Domain.h
@@ -111,6 +111,7 @@ public: // Public variables (need to create accessors instead)
     int Nx,Ny,Nz,N;
     int inlet_layers_x, inlet_layers_y, inlet_layers_z;
     int outlet_layers_x, outlet_layers_y, outlet_layers_z;
+    double porosity;
     RankInfoStruct rank_info;
 
     MPI_Comm Comm;        // MPI Communicator for this domain
@@ -122,6 +123,7 @@ public: // Public variables (need to create accessors instead)
     //**********************************
     // MPI ranks for all 18 neighbors
     //**********************************
+    inline double Porosity() const { return porosity; }
     inline int iproc() const { return rank_info.ix; }
     inline int jproc() const { return rank_info.jy; }
     inline int kproc() const { return rank_info.kz; }
diff --git a/models/MRTModel.cpp b/models/MRTModel.cpp
index fc1fa05f..8bb06fec 100644
--- a/models/MRTModel.cpp
+++ b/models/MRTModel.cpp
@@ -241,8 +241,8 @@ void ScaLBL_MRTModel::Run(){
 			Hs=sumReduce( Dm->Comm, Hs);
 			Xs=sumReduce( Dm->Comm, Xs);
 			if (rank==0) {
-				double h = Lz/double(Nz);
-				double absperm = h*h*mu*sqrt(vax*vax+vay*vay+vaz*vaz)/sqrt(Fx*Fx+Fy*Fy+Fz*Fz);
+				double h = Lz/double((Nz-2)*nprocz);
+				double absperm = h*h*mu*Mask->Porosity()*sqrt(vax*vax+vay*vay+vaz*vaz)/sqrt(Fx*Fx+Fy*Fy+Fz*Fz);
 				printf("     %f\n",absperm);
 				FILE * log_file = fopen("Permeability.csv","a");
 				fprintf(log_file,"%i %.8g %.8g %.8g %.8g %.8g %.8g %.8g %.8g %.8g %.8g %.8g %.8g\n",timestep, Fx, Fy, Fz, mu,