diff --git a/app/models/pool.rb b/app/models/pool.rb
index 8d7a562bd..dae48d7c6 100644
--- a/app/models/pool.rb
+++ b/app/models/pool.rb
@@ -84,7 +84,7 @@ class Pool < ApplicationRecord
       when "created_at"
         q = q.order("pools.created_at desc")
       when "post_count"
-        q = q.order("pools.post_count desc").default_order
+        q = q.order(Arel.sql("cardinality(post_ids) desc")).default_order
       else
         q = q.apply_default_order(params)
       end
@@ -207,7 +207,7 @@ class Pool < ApplicationRecord
     return if is_deleted?
 
     with_lock do
-      update(post_ids: post_ids + [post.id], post_count: post_count + 1)
+      update(post_ids: post_ids + [post.id])
       post.add_pool!(self, true)
     end
   end
@@ -218,7 +218,7 @@ class Pool < ApplicationRecord
 
     with_lock do
       reload
-      update(post_ids: post_ids - [post.id], post_count: post_count - 1)
+      update(post_ids: post_ids - [post.id])
       post.remove_pool!(self)
     end
   end
@@ -255,7 +255,6 @@ class Pool < ApplicationRecord
     end
 
     normalize_post_ids
-    self.post_count = post_ids.size
   end
 
   def synchronize!
@@ -263,6 +262,10 @@ class Pool < ApplicationRecord
     save if will_save_change_to_post_ids?
   end
 
+  def post_count
+    post_ids.size
+  end
+
   def first_post?(post_id)
     page_number(post_id) == 1
   end
@@ -297,7 +300,7 @@ class Pool < ApplicationRecord
   end
 
   def method_attributes
-    super + [:creator_name]
+    super + [:creator_name, :post_count]
   end
 
   def update_category_pseudo_tags_for_posts_async
diff --git a/db/migrate/20181108205842_drop_post_count_from_pools.rb b/db/migrate/20181108205842_drop_post_count_from_pools.rb
new file mode 100644
index 000000000..8e522b0d5
--- /dev/null
+++ b/db/migrate/20181108205842_drop_post_count_from_pools.rb
@@ -0,0 +1,10 @@
+class DropPostCountFromPools < ActiveRecord::Migration[5.2]
+  def up
+    remove_column :pools, :post_count
+  end
+
+  def down
+    add_column :pools, :post_count, :integer, default: 0, null: false
+    Pool.update_all("post_count = cardinality(post_ids)")
+  end
+end
diff --git a/db/structure.sql b/db/structure.sql
index caf555201..7cdd77c0c 100644
--- a/db/structure.sql
+++ b/db/structure.sql
@@ -2564,7 +2564,6 @@ CREATE TABLE public.pools (
     description text,
     is_active boolean DEFAULT true NOT NULL,
     post_ids integer[] DEFAULT '{}'::integer[] NOT NULL,
-    post_count integer DEFAULT 0 NOT NULL,
     is_deleted boolean DEFAULT false NOT NULL,
     created_at timestamp without time zone,
     updated_at timestamp without time zone,
@@ -7579,6 +7578,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20180912185624'),
 ('20180913184128'),
 ('20180916002448'),
-('20181108162204');
+('20181108162204'),
+('20181108205842');