diff --git a/doc/src/fix_damping_cundall.rst b/doc/src/fix_damping_cundall.rst
index 6edba23bcd..4244be539d 100644
--- a/doc/src/fix_damping_cundall.rst
+++ b/doc/src/fix_damping_cundall.rst
@@ -19,9 +19,10 @@ Syntax
   .. parsed-literal::
 
      keyword = *scale*
-       *scale* values = type ratio
+       *scale* values = *type ratio* or *v_name*
          type = atom type (1-N)
          ratio = factor to scale the damping coefficients by
+         v_name = reference to atom style variable *name*
 
 Examples
 """"""""
@@ -30,6 +31,7 @@ Examples
 
    fix 1 all damping/cundall 0.8 0.8
    fix 1 all damping/cundall 0.8 0.5 scale 3 2.5
+   fix a all damping/cundall 0.8 0.5 scale v_radscale
 
 Description
 """""""""""
@@ -58,9 +60,13 @@ particle. Damping is applied component-by-component in each direction
    {T_d}_k = - \gamma_a \, T_k \, \mathrm{sign}(T_k \omega_k)
 
 The larger the coefficients, the faster the kinetic energy is reduced.
+
 If the optional keyword *scale* is used, :math:`\gamma_l` and :math:`\gamma_a`
-can be scaled up or down by the specified factor for atoms of that type.
-It can be used multiple times to adjust :math:`\gamma` for several atom types.
+can be scaled up or down by the specified factor for atoms.  This factor can be
+set for different atom types and thus the *scale* keyword used multiple times
+followed by the atom type and the associated scale factor.  Alternately the
+scaling factor can be computed for each atom (e.g. based on its radius) by
+using an :doc:`atom-style variable <variable>`.
 
 .. Note::
 
diff --git a/doc/src/fix_viscous_sphere.rst b/doc/src/fix_viscous_sphere.rst
index ab0283257d..13463c8c11 100644
--- a/doc/src/fix_viscous_sphere.rst
+++ b/doc/src/fix_viscous_sphere.rst
@@ -18,9 +18,10 @@ Syntax
   .. parsed-literal::
 
      keyword = *scale*
-       *scale* values = type ratio
+       *scale* values = *type ratio* or *v_name*
          type = atom type (1-N)
-         ratio = factor to scale the damping coefficient by
+         ratio = factor to scale the damping coefficients by
+         v_name = reference to atom style variable *name*
 
 Examples
 """"""""
@@ -29,6 +30,7 @@ Examples
 
    fix 1 flow viscous/sphere 0.1
    fix 1 damp viscous/sphere 0.5 scale 3 2.5
+   fix 1 damp viscous/sphere 0.5 scale v_radscale
 
 Description
 """""""""""
@@ -43,9 +45,13 @@ technique.
 
 The damping torque :math:`T_i` is given by :math:`T_i = - \gamma \omega_i`.
 The larger the coefficient, the faster the rotational kinetic energy is reduced.
-If the optional keyword *scale* is used, :math:`\gamma` can be scaled up or
-down by the specified factor for atoms of that type.  It can be used
-multiple times to adjust :math:`\gamma` for several atom types.
+
+If the optional keyword *scale* is used, :math:`\gamma` can be scaled up
+or down by the specified factor for atoms.  This factor can be set for
+different atom types and thus the *scale* keyword used multiple times
+followed by the atom type and the associated scale factor.  Alternately
+the scaling factor can be computed for each atom (e.g. based on its
+radius) by using an :doc:`atom-style variable <variable>`.
 
 .. note::
 
diff --git a/src/EXTRA-FIX/fix_viscous_sphere.cpp b/src/EXTRA-FIX/fix_viscous_sphere.cpp
index fc98f71b41..6131060bac 100644
--- a/src/EXTRA-FIX/fix_viscous_sphere.cpp
+++ b/src/EXTRA-FIX/fix_viscous_sphere.cpp
@@ -14,19 +14,29 @@
 #include "fix_viscous_sphere.h"
 
 #include "atom.h"
+#include "comm.h"
 #include "error.h"
+#include "input.h"
+#include "memory.h"
+#include "modify.h"
 #include "respa.h"
 #include "update.h"
+#include "variable.h"
 
 #include <cstring>
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
 
+// type of scaling
+
+enum { NONE, TYPE, VARIABLE };
+
 /* ---------------------------------------------------------------------- */
 
-FixViscousSphere::FixViscousSphere(LAMMPS *lmp, int narg, char **arg) :
-    Fix(lmp, narg, arg), gamma(nullptr)
+FixViscousSphere::FixViscousSphere(LAMMPS *_lmp, int narg, char **arg) :
+    Fix(_lmp, narg, arg), scalegamma(nullptr), scaleval(nullptr), scalevarid(nullptr),
+    scalestyle(NONE)
 {
   dynamic_group_allow = 1;
 
@@ -34,22 +44,41 @@ FixViscousSphere::FixViscousSphere(LAMMPS *lmp, int narg, char **arg) :
 
   if (narg < 4) error->all(FLERR, "Illegal fix viscous/sphere command");
 
-  double gamma_one = utils::numeric(FLERR, arg[3], false, lmp);
-  gamma = new double[atom->ntypes + 1];
-  for (int i = 1; i <= atom->ntypes; i++) gamma[i] = gamma_one;
+  gamma = utils::numeric(FLERR, arg[3], false, lmp);
 
   // optional args
 
   int iarg = 4;
   while (iarg < narg) {
     if (strcmp(arg[iarg], "scale") == 0) {
-      if (iarg + 3 > narg) error->all(FLERR, "Illegal fix viscous/sphere command");
-      int itype = utils::inumeric(FLERR, arg[iarg + 1], false, lmp);
-      double scale = utils::numeric(FLERR, arg[iarg + 2], false, lmp);
-      if (itype <= 0 || itype > atom->ntypes)
-        error->all(FLERR, "Illegal fix viscous/sphere command");
-      gamma[itype] = gamma_one * scale;
-      iarg += 3;
+      if (iarg + 2 > narg) error->all(FLERR, "Illegal fix viscous/sphere command");
+      if (utils::strmatch(arg[iarg + 1], "^v_")) {
+        if (scalestyle != NONE) error->all(FLERR, "Must use only one style of scaling");
+        scalevarid = utils::strdup(arg[iarg + 1] + 2);
+        int ivariable = input->variable->find(scalevarid);
+        if (ivariable < 0)
+          error->all(FLERR, "Variable name {} for fix viscous/sphere does not exist", scalevarid);
+        if (input->variable->atomstyle(ivariable) == 0)
+          error->all(FLERR, "Fix viscous/scale variable {} is not atom-style variable", scalevarid);
+        scalestyle = VARIABLE;
+        memory->destroy(scaleval);
+        memory->create(scaleval, atom->nmax, "fix_viscous/sphere:scaleval");
+        iarg += 2;
+      } else {
+        if (scalestyle == VARIABLE) error->all(FLERR, "Must use only one style of scaling");
+        if (iarg + 3 > narg) error->all(FLERR, "Illegal fix viscous/sphere command");
+        if (!scalegamma) {
+          scalegamma = new double[atom->ntypes + 1];
+          for (int i = 1; i <= atom->ntypes; i++) scalegamma[i] = 1.0;
+        }
+        int itype = utils::inumeric(FLERR, arg[iarg + 1], false, lmp);
+        double scale = utils::numeric(FLERR, arg[iarg + 2], false, lmp);
+        if ((itype < 1) || (itype > atom->ntypes))
+          error->all(FLERR, "Atom type {} out of range for fix viscous/sphere command:", itype);
+        scalegamma[itype] = scale;
+        scalestyle = TYPE;
+        iarg += 3;
+      }
     } else
       error->all(FLERR, "Illegal fix viscous/sphere command");
   }
@@ -62,7 +91,9 @@ FixViscousSphere::FixViscousSphere(LAMMPS *lmp, int narg, char **arg) :
 
 FixViscousSphere::~FixViscousSphere()
 {
-  delete[] gamma;
+  memory->destroy(scaleval);
+  delete[] scalegamma;
+  delete[] scalevarid;
 }
 
 /* ---------------------------------------------------------------------- */
@@ -86,6 +117,22 @@ void FixViscousSphere::init()
     ilevel_respa = max_respa = ((Respa *) update->integrate)->nlevels - 1;
     if (respa_level >= 0) ilevel_respa = MIN(respa_level, max_respa);
   }
+
+  bool fflag = false;
+  for (auto ifix : modify->get_fix_list()) {
+    if (fflag && (comm->me == 0) && (ifix->setmask() & POST_FORCE))
+      error->warning(FLERR, "Fix {} alters forces after fix viscous/sphere", ifix->id);
+    if (ifix == this) fflag = true;
+  }
+
+  if (scalestyle == VARIABLE) {
+    int ivariable = input->variable->find(scalevarid);
+    if (ivariable < 0)
+      error->all(FLERR, "Variable name {} for fix viscous/sphere does not exist", scalevarid);
+    if (input->variable->atomstyle(ivariable) == 0)
+      error->all(FLERR, "Fix viscous/sphere variable {} is not atom-style variable", scalevarid);
+    scalevar = ivariable;
+  }
 }
 
 /* ---------------------------------------------------------------------- */
@@ -123,10 +170,20 @@ void FixViscousSphere::post_force(int /*vflag*/)
   int nlocal = atom->nlocal;
 
   double drag;
+  if (scalestyle == VARIABLE) {
+    memory->grow(scaleval, atom->nmax, "fix_viscous/sphere:scaleval");
+    input->variable->compute_atom(scalevar, igroup, scaleval, 1, 0);
+  }
 
   for (int i = 0; i < nlocal; i++)
     if (mask[i] & groupbit) {
-      drag = gamma[type[i]];
+      if (scalestyle == TYPE) {
+        drag = gamma * scalegamma[type[i]];
+      } else if (scalestyle == VARIABLE) {
+        drag = gamma * scaleval[i];
+      } else {    // scalestyle == NONE
+        drag = gamma;
+      }
       torque[i][0] -= drag * omega[i][0];
       torque[i][1] -= drag * omega[i][1];
       torque[i][2] -= drag * omega[i][2];
@@ -146,3 +203,15 @@ void FixViscousSphere::min_post_force(int vflag)
 {
   post_force(vflag);
 }
+
+/* ---------------------------------------------------------------------- */
+
+double FixViscousSphere::memory_usage()
+{
+  if (scalestyle == VARIABLE)
+    return (double) sizeof(double) * atom->nmax;
+  else if (scalestyle == TYPE)
+    return (double) sizeof(double) * atom->ntypes;
+  else
+    return 0.0;
+}
diff --git a/src/EXTRA-FIX/fix_viscous_sphere.h b/src/EXTRA-FIX/fix_viscous_sphere.h
index e5c90bda25..fc85deee86 100644
--- a/src/EXTRA-FIX/fix_viscous_sphere.h
+++ b/src/EXTRA-FIX/fix_viscous_sphere.h
@@ -35,9 +35,12 @@ class FixViscousSphere : public Fix {
   void post_force(int);
   void post_force_respa(int, int, int);
   void min_post_force(int);
+  double memory_usage();
 
  protected:
-  double *gamma;
+  double gamma, *scalegamma, *scaleval;
+  const char *scalevarid;
+  int scalestyle, scalevar;
   int ilevel_respa;
 };
 
diff --git a/src/GRANULAR/fix_damping_cundall.cpp b/src/GRANULAR/fix_damping_cundall.cpp
index 491d43f549..ee4cfaa950 100644
--- a/src/GRANULAR/fix_damping_cundall.cpp
+++ b/src/GRANULAR/fix_damping_cundall.cpp
@@ -14,19 +14,29 @@
 #include "fix_damping_cundall.h"
 
 #include "atom.h"
+#include "comm.h"
 #include "error.h"
+#include "input.h"
+#include "memory.h"
+#include "modify.h"
 #include "respa.h"
 #include "update.h"
+#include "variable.h"
 
 #include <cstring>
 
 using namespace LAMMPS_NS;
 using namespace FixConst;
 
+// type of scaling
+
+enum { NONE, TYPE, VARIABLE };
+
 /* ---------------------------------------------------------------------- */
 
-FixDampingCundall::FixDampingCundall(LAMMPS *lmp, int narg, char **arg) :
-    Fix(lmp, narg, arg), gamma_lin(nullptr), gamma_ang(nullptr)
+FixDampingCundall::FixDampingCundall(LAMMPS *_lmp, int narg, char **arg) :
+    Fix(_lmp, narg, arg), scalegamma(nullptr), scaleval(nullptr), scalevarid(nullptr),
+    scalestyle(NONE)
 {
   dynamic_group_allow = 1;
 
@@ -34,28 +44,42 @@ FixDampingCundall::FixDampingCundall(LAMMPS *lmp, int narg, char **arg) :
 
   if (narg < 5) error->all(FLERR, "Illegal fix damping/cundall command");
 
-  double gamma_lin_one = utils::numeric(FLERR, arg[3], false, lmp);
-  double gamma_ang_one = utils::numeric(FLERR, arg[4], false, lmp);
-  gamma_lin = new double[atom->ntypes + 1];
-  gamma_ang = new double[atom->ntypes + 1];
-  for (int i = 1; i <= atom->ntypes; i++) {
-    gamma_lin[i] = gamma_lin_one;
-    gamma_ang[i] = gamma_ang_one;
-  }
+  gamma_lin = utils::numeric(FLERR, arg[3], false, lmp);
+  gamma_ang = utils::numeric(FLERR, arg[4], false, lmp);
 
   // optional args
 
   int iarg = 5;
   while (iarg < narg) {
     if (strcmp(arg[iarg], "scale") == 0) {
-      if (iarg + 3 > narg) error->all(FLERR, "Illegal fix damping/cundall command");
-      int itype = utils::inumeric(FLERR, arg[iarg + 1], false, lmp);
-      double scale = utils::numeric(FLERR, arg[iarg + 2], false, lmp);
-      if (itype <= 0 || itype > atom->ntypes)
-        error->all(FLERR, "Illegal fix damping/cundall command");
-      gamma_lin[itype] = gamma_lin_one * scale;
-      gamma_ang[itype] = gamma_ang_one * scale;
-      iarg += 3;
+      if (iarg + 2 > narg) error->all(FLERR, "Illegal fix damping/cundall command");
+      if (utils::strmatch(arg[iarg + 1], "^v_")) {
+        if (scalestyle != NONE) error->all(FLERR, "Must use only one style of scaling");
+        scalevarid = utils::strdup(arg[iarg + 1] + 2);
+        int ivariable = input->variable->find(scalevarid);
+        if (ivariable < 0)
+          error->all(FLERR, "Variable name {} for fix damping/cundall does not exist", scalevarid);
+        if (input->variable->atomstyle(ivariable) == 0)
+          error->all(FLERR, "Fix viscous/scale variable {} is not atom-style variable", scalevarid);
+        scalestyle = VARIABLE;
+        memory->destroy(scaleval);
+        memory->create(scaleval, atom->nmax, "fix_damping/cundall:scaleval");
+        iarg += 2;
+      } else {
+        if (scalestyle == VARIABLE) error->all(FLERR, "Must use only one style of scaling");
+        if (iarg + 3 > narg) error->all(FLERR, "Illegal fix damping/cundall command");
+        if (!scalegamma) {
+          scalegamma = new double[atom->ntypes + 1];
+          for (int i = 1; i <= atom->ntypes; i++) scalegamma[i] = 1.0;
+        }
+        int itype = utils::inumeric(FLERR, arg[iarg + 1], false, lmp);
+        double scale = utils::numeric(FLERR, arg[iarg + 2], false, lmp);
+        if ((itype < 1) || (itype > atom->ntypes))
+          error->all(FLERR, "Atom type {} out of range for fix damping/cundall command:", itype);
+        scalegamma[itype] = scale;
+        scalestyle = TYPE;
+        iarg += 3;
+      }
     } else
       error->all(FLERR, "Illegal fix damping/cundall command");
   }
@@ -68,8 +92,9 @@ FixDampingCundall::FixDampingCundall(LAMMPS *lmp, int narg, char **arg) :
 
 FixDampingCundall::~FixDampingCundall()
 {
-  delete[] gamma_lin;
-  delete[] gamma_ang;
+  memory->destroy(scaleval);
+  delete[] scalegamma;
+  delete[] scalevarid;
 }
 
 /* ---------------------------------------------------------------------- */
@@ -93,6 +118,22 @@ void FixDampingCundall::init()
     ilevel_respa = max_respa = ((Respa *) update->integrate)->nlevels - 1;
     if (respa_level >= 0) ilevel_respa = MIN(respa_level, max_respa);
   }
+
+  bool fflag = false;
+  for (auto ifix : modify->get_fix_list()) {
+    if (fflag && (comm->me == 0) && (ifix->setmask() & POST_FORCE))
+      error->warning(FLERR, "Fix {} alters forces after fix damping/cundall", ifix->id);
+    if (ifix == this) fflag = true;
+  }
+
+  if (scalestyle == VARIABLE) {
+    int ivariable = input->variable->find(scalevarid);
+    if (ivariable < 0)
+      error->all(FLERR, "Variable name {} for fix damping/cundall does not exist", scalevarid);
+    if (input->variable->atomstyle(ivariable) == 0)
+      error->all(FLERR, "Fix damping/cundall variable {} is not atom-style variable", scalevarid);
+    scalevar = ivariable;
+  }
 }
 
 /* ---------------------------------------------------------------------- */
@@ -140,10 +181,23 @@ void FixDampingCundall::post_force(int /*vflag*/)
   int signf0, signf1, signf2;
   int signt0, signt1, signt2;
 
+  if (scalestyle == VARIABLE) {
+    memory->grow(scaleval, atom->nmax, "fix_damping/cundall:scaleval");
+    input->variable->compute_atom(scalevar, igroup, scaleval, 1, 0);
+  }
+
   for (int i = 0; i < nlocal; i++)
     if (mask[i] & groupbit) {
-      gamma_l = gamma_lin[type[i]];
-      gamma_a = gamma_ang[type[i]];
+      if (scalestyle == TYPE) {
+        gamma_l = gamma_lin * scalegamma[type[i]];
+        gamma_a = gamma_ang * scalegamma[type[i]];
+      } else if (scalestyle == VARIABLE) {
+        gamma_l = gamma_lin * scaleval[i];
+        gamma_a = gamma_ang * scaleval[i];
+      } else {    // scalestyle NONE
+        gamma_l = gamma_lin;
+        gamma_a = gamma_ang;
+      }
 
       signf0 = (f[i][0] * v[i][0] >= 0.0) ? 1.0 : -1.0;
       signf1 = (f[i][1] * v[i][1] >= 0.0) ? 1.0 : -1.0;
@@ -174,3 +228,15 @@ void FixDampingCundall::min_post_force(int vflag)
 {
   post_force(vflag);
 }
+
+/* ---------------------------------------------------------------------- */
+
+double FixDampingCundall::memory_usage()
+{
+  if (scalestyle == VARIABLE)
+    return (double) sizeof(double) * atom->nmax;
+  else if (scalestyle == TYPE)
+    return 2.0 * sizeof(double) * atom->ntypes;
+  else
+    return 0.0;
+}
diff --git a/src/GRANULAR/fix_damping_cundall.h b/src/GRANULAR/fix_damping_cundall.h
index b51a84b3da..aed7e979cc 100644
--- a/src/GRANULAR/fix_damping_cundall.h
+++ b/src/GRANULAR/fix_damping_cundall.h
@@ -35,9 +35,12 @@ class FixDampingCundall : public Fix {
   void post_force(int);
   void post_force_respa(int, int, int);
   void min_post_force(int);
+  double memory_usage();
 
  protected:
-  double *gamma_lin, *gamma_ang;
+  double gamma_lin, gamma_ang, *scalegamma, *scaleval;
+  const char *scalevarid;
+  int scalestyle, scalevar;
   int ilevel_respa;
 };