diff --git a/src/app/commands/cmd_undo_history.cpp b/src/app/commands/cmd_undo_history.cpp
index ded7f7c87..4eef43b8c 100644
--- a/src/app/commands/cmd_undo_history.cpp
+++ b/src/app/commands/cmd_undo_history.cpp
@@ -1,5 +1,5 @@
 // Aseprite
-// Copyright (C) 2015-2016  David Capello
+// Copyright (C) 2015-2017  David Capello
 //
 // This program is distributed under the terms of
 // the End-User License Agreement for Aseprite.
@@ -52,8 +52,9 @@ public:
   };
 
   UndoHistoryWindow(Context* ctx)
-    : m_ctx(ctx),
-      m_document(nullptr) {
+    : m_ctx(ctx)
+    , m_document(nullptr) {
+    m_title = text();
     actions()->Change.connect(&UndoHistoryWindow::onChangeAction, this);
   }
 
@@ -168,6 +169,10 @@ private:
     refillList(history);
   }
 
+  void onTotalUndoSizeChange(DocumentUndo* history) override {
+    updateTitle();
+  }
+
   void attachDocument(app::Document* document) {
     detachDocument();
 
@@ -179,6 +184,7 @@ private:
     history->add_observer(this);
 
     refillList(history);
+    updateTitle();
   }
 
   void detachDocument() {
@@ -188,6 +194,7 @@ private:
     clearList();
     m_document->undoHistory()->remove_observer(this);
     m_document = nullptr;
+    updateTitle();
   }
 
   void clearList() {
@@ -232,9 +239,19 @@ private:
     }
   }
 
+  void updateTitle() {
+    if (!m_document)
+      setText(m_title);
+    else
+      setTextf("%s (%s)",
+               m_title.c_str(),
+               base::get_pretty_memory_size(m_document->undoHistory()->totalUndoSize()).c_str());
+  }
+
   Context* m_ctx;
   app::Document* m_document;
   doc::frame_t m_frame;
+  std::string m_title;
 };
 
 class UndoHistoryCommand : public Command {
diff --git a/src/app/document_undo.cpp b/src/app/document_undo.cpp
index cdd205711..973361ec3 100644
--- a/src/app/document_undo.cpp
+++ b/src/app/document_undo.cpp
@@ -24,6 +24,7 @@
 #include <stdexcept>
 
 #define UNDO_TRACE(...)
+#define STATE_CMD(state) (static_cast<CmdTransaction*>(state->cmd()))
 
 namespace app {
 
@@ -59,6 +60,7 @@ void DocumentUndo::add(CmdTransaction* cmd)
   m_totalUndoSize += cmd->memSize();
 
   notify_observers(&DocumentUndoObserver::onAddUndoState, this);
+  notify_observers(&DocumentUndoObserver::onTotalUndoSizeChange, this);
 
   if (App::instance()) {
     const size_t undoLimitSize =
@@ -97,14 +99,34 @@ bool DocumentUndo::canRedo() const
 
 void DocumentUndo::undo()
 {
-  m_undoHistory.undo();
-  notify_observers(&DocumentUndoObserver::onAfterUndo, this);
+  const undo::UndoState* state = nextUndo();
+  ASSERT(state);
+  const Cmd* cmd = STATE_CMD(state);
+  size_t oldSize = m_totalUndoSize;
+  m_totalUndoSize -= cmd->memSize();
+  {
+    m_undoHistory.undo();
+    notify_observers(&DocumentUndoObserver::onAfterUndo, this);
+  }
+  m_totalUndoSize += cmd->memSize();
+  if (m_totalUndoSize != oldSize)
+    notify_observers(&DocumentUndoObserver::onTotalUndoSizeChange, this);
 }
 
 void DocumentUndo::redo()
 {
-  m_undoHistory.redo();
-  notify_observers(&DocumentUndoObserver::onAfterRedo, this);
+  const undo::UndoState* state = nextRedo();
+  ASSERT(state);
+  const Cmd* cmd = STATE_CMD(state);
+  size_t oldSize = m_totalUndoSize;
+  m_totalUndoSize -= cmd->memSize();
+  {
+    m_undoHistory.redo();
+    notify_observers(&DocumentUndoObserver::onAfterRedo, this);
+  }
+  m_totalUndoSize += cmd->memSize();
+  if (m_totalUndoSize != oldSize)
+    notify_observers(&DocumentUndoObserver::onTotalUndoSizeChange, this);
 }
 
 void DocumentUndo::clearRedo()
@@ -133,7 +155,7 @@ std::string DocumentUndo::nextUndoLabel() const
 {
   const undo::UndoState* state = nextUndo();
   if (state)
-    return static_cast<Cmd*>(state->cmd())->label();
+    return STATE_CMD(state)->label();
   else
     return "";
 }
@@ -142,7 +164,7 @@ std::string DocumentUndo::nextRedoLabel() const
 {
   const undo::UndoState* state = nextRedo();
   if (state)
-    return static_cast<const Cmd*>(state->cmd())->label();
+    return STATE_CMD(state)->label();
   else
     return "";
 }
@@ -151,8 +173,7 @@ SpritePosition DocumentUndo::nextUndoSpritePosition() const
 {
   const undo::UndoState* state = nextUndo();
   if (state)
-    return static_cast<const CmdTransaction*>(state->cmd())
-      ->spritePositionBeforeExecute();
+    return STATE_CMD(state)->spritePositionBeforeExecute();
   else
     return SpritePosition();
 }
@@ -161,8 +182,7 @@ SpritePosition DocumentUndo::nextRedoSpritePosition() const
 {
   const undo::UndoState* state = nextRedo();
   if (state)
-    return static_cast<const CmdTransaction*>(state->cmd())
-      ->spritePositionAfterExecute();
+    return STATE_CMD(state)->spritePositionAfterExecute();
   else
     return SpritePosition();
 }
@@ -171,7 +191,7 @@ Cmd* DocumentUndo::lastExecutedCmd() const
 {
   const undo::UndoState* state = m_undoHistory.currentState();
   if (state)
-    return static_cast<Cmd*>(state->cmd());
+    return STATE_CMD(state);
   else
     return NULL;
 }
@@ -179,6 +199,17 @@ Cmd* DocumentUndo::lastExecutedCmd() const
 void DocumentUndo::moveToState(const undo::UndoState* state)
 {
   m_undoHistory.moveTo(state);
+
+  // Recalculate the total undo size
+  size_t oldSize = m_totalUndoSize;
+  m_totalUndoSize = 0;
+  const undo::UndoState* s = m_undoHistory.firstState();
+  while (s) {
+    m_totalUndoSize += STATE_CMD(s)->memSize();
+    s = s->next();
+  }
+  if (m_totalUndoSize != oldSize)
+    notify_observers(&DocumentUndoObserver::onTotalUndoSizeChange, this);
 }
 
 const undo::UndoState* DocumentUndo::nextUndo() const
@@ -197,7 +228,7 @@ const undo::UndoState* DocumentUndo::nextRedo() const
 
 void DocumentUndo::onDeleteUndoState(undo::UndoState* state)
 {
-  Cmd* cmd = static_cast<Cmd*>(state->cmd());
+  Cmd* cmd = STATE_CMD(state);
 
   UNDO_TRACE("UNDO: Deleting undo state <%s> of %s from %s\n",
              cmd->label().c_str(),
diff --git a/src/app/document_undo.h b/src/app/document_undo.h
index 34c982a32..7acb62902 100644
--- a/src/app/document_undo.h
+++ b/src/app/document_undo.h
@@ -32,6 +32,8 @@ namespace app {
   public:
     DocumentUndo();
 
+    size_t totalUndoSize() const { return m_totalUndoSize; }
+
     void setContext(doc::Context* ctx);
 
     void add(CmdTransaction* cmd);
diff --git a/src/app/document_undo_observer.h b/src/app/document_undo_observer.h
index 000746991..7bfcbd057 100644
--- a/src/app/document_undo_observer.h
+++ b/src/app/document_undo_observer.h
@@ -25,6 +25,7 @@ class DocumentUndo;
     virtual void onAfterUndo(DocumentUndo* history) = 0;
     virtual void onAfterRedo(DocumentUndo* history) = 0;
     virtual void onClearRedo(DocumentUndo* history) = 0;
+    virtual void onTotalUndoSizeChange(DocumentUndo* history) = 0;
   };
 
 } // namespace app