diff --git a/app/controllers/quantities_controller.rb b/app/controllers/quantities_controller.rb
index e92cee4..fe5213a 100644
--- a/app/controllers/quantities_controller.rb
+++ b/app/controllers/quantities_controller.rb
@@ -2,7 +2,7 @@ class QuantitiesController < ApplicationController
   before_action only: :new do
     find_quantity if params[:id].present?
   end
-  before_action :find_quantity, only: [:edit, :update, :rebase, :destroy]
+  before_action :find_quantity, only: [:edit, :update, :reparent, :destroy]
 
   before_action except: :index do
     raise AccessForbidden unless current_user.at_least(:active)
@@ -39,6 +39,18 @@ class QuantitiesController < ApplicationController
     end
   end
 
+  def reparent
+    permitted = params.require(:quantity).permit(:parent_id)
+    @previous_ancestors = @quantity.ancestors
+
+    @quantity.update!(permitted)
+
+    @ancestors = @quantity.ancestors
+    @quantity.depth = @ancestors.length
+    @self_and_progenies = @quantity.progenies.unshift(@quantity)
+    @before = @self_and_progenies.last.successive
+  end
+
   def destroy
     @quantity.destroy!
     @ancestors = @quantity.ancestors
diff --git a/app/models/quantity.rb b/app/models/quantity.rb
index ee4eabb..ebb22dd 100644
--- a/app/models/quantity.rb
+++ b/app/models/quantity.rb
@@ -29,8 +29,8 @@ class Quantity < ApplicationRecord
       numbered.project(
         numbered[Arel.star],
         numbered.cast(numbered[:child_number], 'BINARY').as('path'),
-        Arel::Nodes.build_quoted(0).as('depth')
-      ).where(numbered[:parent_id].eq(root)),
+        Arel::Nodes.build_quoted(root&.depth&.succ || 0).as('depth')
+      ).where(numbered[:parent_id].eq(root&.id)),
       numbered.project(
         numbered[Arel.star],
         arel_table[:path].concat(numbered[:child_number]),
@@ -70,8 +70,8 @@ class Quantity < ApplicationRecord
     parent_id.nil?
   end
 
-  # Return: self, ancestors and successive record in order of appearance,
-  # including :depth attribute. Used for partial view reload.
+  # Return: successive record in order of appearance, including :depth
+  # attribute. Used for partial view reload.
   def successive
     quantities = Quantity.arel_table
 
@@ -90,9 +90,13 @@ class Quantity < ApplicationRecord
       selected.project(selected[Arel.star]).where(selected[:id].eq(quantity.id)),
       selected.project(selected[Arel.star])
         .join(arel_table).on(arel_table[:id].eq(selected[:parent_id]))
-    ]).ordered(root: quantity.id)
+    ]).ordered(root: quantity)
   }
 
+  def progenies
+    user.quantities.progenies(self).to_a
+  end
+
   # Return: ancestors of (possibly destroyed) self; include depths, also on
   # self (unless destroyed)
   def ancestors
@@ -111,7 +115,7 @@ class Quantity < ApplicationRecord
         ))
     ]).select(ancestors[Arel.star]).from(ancestors).to_a.then do |records|
       records.map(&:depth).min&.abs.then do |maxdepth|
-        self.depth = (maxdepth || -1) + 1 unless frozen?
+        self.depth = maxdepth&.succ || 0 unless frozen?
         records.each { |r| r.depth += maxdepth }
       end
     end
diff --git a/app/views/quantities/reparent.turbo_stream.erb b/app/views/quantities/reparent.turbo_stream.erb
new file mode 100644
index 0000000..3023389
--- /dev/null
+++ b/app/views/quantities/reparent.turbo_stream.erb
@@ -0,0 +1,9 @@
+<% @self_and_progenies.each do |q| %>
+  <%= turbo_stream.remove q %>
+<% end %>
+<% @previous_ancestors.union(@ancestors).map do |ancestor| %>
+  <%= turbo_stream.replace ancestor %>
+<% end %>
+<% @self_and_progenies.each do |q| %>
+  <%= @before.nil? ? turbo_stream.append(:quantities, q) : turbo_stream.before(@before, q) %>
+<% end %>
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 2f1bb22..041a972 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -68,6 +68,7 @@ en:
       destroy: Delete
     index:
       new_quantity: Add quantity
+      top_level_drop: Drop here to reposition into top-level quantity
     create:
       success: Created new quantity "%{quantity}"
     update:
diff --git a/config/routes.rb b/config/routes.rb
index 5bab666..25aa414 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -1,6 +1,6 @@
 Rails.application.routes.draw do
   resources :quantities, except: [:show], path_names: {new: '(/:id)/new'} do
-    member { post :rebase }
+    member { post :reparent }
   end
 
   resources :units, except: [:show], path_names: {new: '(/:id)/new'} do