diff --git a/pybamm/models/submodels/electrolyte_conductivity/surface_potential_form/full_surface_form_conductivity.py b/pybamm/models/submodels/electrolyte_conductivity/surface_potential_form/full_surface_form_conductivity.py
index 50f36f83f9..cceb88f83e 100644
--- a/pybamm/models/submodels/electrolyte_conductivity/surface_potential_form/full_surface_form_conductivity.py
+++ b/pybamm/models/submodels/electrolyte_conductivity/surface_potential_form/full_surface_form_conductivity.py
@@ -272,13 +272,11 @@ def set_rhs(self, variables):
         domain, Domain = self.domain_Domain
 
         T = variables[f"{Domain} electrode temperature [K]"]
-
         C_dl = self.domain_param.C_dl(T)
 
         delta_phi = variables[f"{Domain} electrode surface potential difference [V]"]
         i_e = variables[f"{Domain} electrolyte current density [A.m-2]"]
 
-        # Variable summing all of the interfacial current densities
         sum_a_j = variables[
             f"Sum of {domain} electrode volumetric "
             "interfacial current densities [A.m-3]"
diff --git a/pybamm/models/submodels/electrolyte_conductivity/surface_potential_form/leading_surface_form_conductivity.py b/pybamm/models/submodels/electrolyte_conductivity/surface_potential_form/leading_surface_form_conductivity.py
index 629f764b0c..c7b47cdd37 100644
--- a/pybamm/models/submodels/electrolyte_conductivity/surface_potential_form/leading_surface_form_conductivity.py
+++ b/pybamm/models/submodels/electrolyte_conductivity/surface_potential_form/leading_surface_form_conductivity.py
@@ -86,24 +86,26 @@ def __init__(self, param, domain, options=None):
 
     def set_rhs(self, variables):
         domain = self.domain
+        T = variables[f"X-averaged {domain} electrode temperature [K]"]
+        C_dl = self.domain_param.C_dl(T)
+
+        delta_phi = variables[
+            f"X-averaged {domain} electrode surface potential difference [V]"
+        ]
+
         sum_a_j = variables[
             f"Sum of x-averaged {domain} electrode volumetric "
             "interfacial current densities [A.m-3]"
         ]
-
         sum_a_j_av = variables[
             f"X-averaged {domain} electrode total volumetric "
             "interfacial current density [A.m-3]"
         ]
-        delta_phi = variables[
-            f"X-averaged {domain} electrode surface potential difference [V]"
+        a = variables[
+            f"X-averaged {domain} electrode surface area to volume ratio [m-1]"
         ]
 
-        T = variables[f"X-averaged {domain} electrode temperature [K]"]
-
-        C_dl = self.domain_param.C_dl(T)
-
-        self.rhs[delta_phi] = 1 / C_dl * (sum_a_j_av - sum_a_j)
+        self.rhs[delta_phi] = 1 / (a * C_dl) * (sum_a_j_av - sum_a_j)
 
 
 class LeadingOrderAlgebraic(BaseLeadingOrderSurfaceForm):