diff --git a/NEWS b/NEWS
index a86212c0f71ad1f584c233dee07982632ac2fca3..4dc6ed9966971aff652c574a2dd0e52bc2c8084d 100644
--- a/NEWS
+++ b/NEWS
@@ -1,6 +1,10 @@
 New in spot 2.3.1.dev (not yet released)
 
-  Nothing yet.
+  Tools:
+
+  - In tools that output automata the number of atomic propositions
+    can be output using --stats=%x (output automaton) or --stats=%X
+    (input automaton).
 
 New in spot 2.3.1 (2017-02-20)
 
diff --git a/bin/common_aoutput.cc b/bin/common_aoutput.cc
index ce0944b2c20b039584b9ba4c018778644a7a9b77..e8011b30fe9ee227d61a05f0315edad31e1a5010 100644
--- a/bin/common_aoutput.cc
+++ b/bin/common_aoutput.cc
@@ -1,6 +1,6 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2012, 2013, 2014, 2015, 2016 Laboratoire de Recherche
-// et Développement de l'Epita (LRDE).
+// Copyright (C) 2012-2017 Laboratoire de Recherche et Développement
+// de l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
 //
@@ -193,6 +193,8 @@ static const argp_option io_options[] =
       "wall-clock time elapsed in seconds (excluding parsing)", 0 },
     { "%W, %w", 0, nullptr, OPTION_DOC | OPTION_NO_USAGE,
       "one word accepted by the automaton", 0 },
+    { "%X, %x", 0, nullptr, OPTION_DOC | OPTION_NO_USAGE,
+      "number of atomic propositions declared in the automaton", 0 },
     { "%%", 0, nullptr, OPTION_DOC | OPTION_NO_USAGE,
       "a single %", 0 },
     { "%<", 0, nullptr, OPTION_DOC | OPTION_NO_USAGE,
@@ -228,6 +230,8 @@ static const argp_option o_options[] =
       "number of transitions", 0 },
     { "%a", 0, nullptr, OPTION_DOC | OPTION_NO_USAGE,
       "number of acceptance sets", 0 },
+    { "%b", 0, nullptr, OPTION_DOC | OPTION_NO_USAGE,
+      "number of acceptance sets", 0 },
     { "%g", 0, nullptr, OPTION_DOC | OPTION_NO_USAGE,
       "acceptance condition (in HOA syntax)", 0 },
     { "%c, %[LETTERS]c", 0, nullptr, OPTION_DOC | OPTION_NO_USAGE,
@@ -250,6 +254,8 @@ static const argp_option o_options[] =
       "wall-clock time elapsed in seconds (excluding parsing)", 0 },
     { "%w", 0, nullptr, OPTION_DOC | OPTION_NO_USAGE,
       "one word accepted by the output automaton", 0 },
+    { "%x", 0, nullptr, OPTION_DOC | OPTION_NO_USAGE,
+      "number of atomic propositions declared in the automaton", 0 },
     { "%%", 0, nullptr, OPTION_DOC | OPTION_NO_USAGE,
       "a single %", 0 },
     { nullptr, 0, nullptr, 0, nullptr, 0 }
@@ -361,6 +367,7 @@ hoa_stat_printer::hoa_stat_printer(std::ostream& os, const char* format,
       declare('S', &haut_states_);
       declare('T', &haut_trans_);
       declare('W', &haut_word_);
+      declare('X', &haut_ap_size_);
     }
   declare('<', &csv_prefix_);
   declare('>', &csv_suffix_);
@@ -372,6 +379,7 @@ hoa_stat_printer::hoa_stat_printer(std::ostream& os, const char* format,
   declare('h', &output_aut_);
   declare('m', &aut_name_);
   declare('w', &aut_word_);
+  declare('x', &aut_ap_size_);
 }
 
 std::ostream&
@@ -467,6 +475,8 @@ hoa_stat_printer::print(const spot::const_parsed_aut_ptr& haut,
               haut_word_.val().clear();
             }
         }
+      if (has('X'))
+        haut_ap_size_ = haut->aut->ap().size();
     }
 
   if (has('m'))
@@ -490,6 +500,8 @@ hoa_stat_printer::print(const spot::const_parsed_aut_ptr& haut,
           aut_word_.val().clear();
         }
     }
+  if (has('x'))
+    aut_ap_size_ = aut->ap().size();
 
   auto& res = this->spot::stat_printer::print(aut, f, run_time);
   // Make sure we do not store the automaton until the next one is
diff --git a/bin/common_aoutput.hh b/bin/common_aoutput.hh
index 9a10b07459b3abb76c3b9bf86fc2510daf4a4163..f22244242a1ec2a79539bf7170b9bce27988092f 100644
--- a/bin/common_aoutput.hh
+++ b/bin/common_aoutput.hh
@@ -1,6 +1,6 @@
 // -*- coding: utf-8 -*-
-// Copyright (C) 2014, 2015, 2016 Laboratoire de Recherche et
-// Développement de l'Epita (LRDE).
+// Copyright (C) 2014-2017 Laboratoire de Recherche et Développement
+// de l'Epita (LRDE).
 //
 // This file is part of Spot, a model checking library.
 //
@@ -144,6 +144,8 @@ private:
   spot::printable_value<unsigned> haut_edges_;
   spot::printable_value<unsigned> haut_trans_;
   spot::printable_value<unsigned> haut_acc_;
+  spot::printable_value<unsigned> haut_ap_size_;
+  spot::printable_value<unsigned> aut_ap_size_;
   spot::printable_scc_info haut_scc_;
   spot::printable_value<unsigned> haut_deterministic_;
   spot::printable_value<unsigned> haut_nondetstates_;
diff --git a/tests/core/remprop.test b/tests/core/remprop.test
index 09e28d7ce6e75b6e57bb6b8b47e8b16c8a3aabc9..e423c4784ffa3cc7d6a0fd6657e364e3d072af75 100755
--- a/tests/core/remprop.test
+++ b/tests/core/remprop.test
@@ -1,6 +1,6 @@
 #! /bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2015, 2016 Laboratoire de Recherche et Développement de
+# Copyright (C) 2015-2017 Laboratoire de Recherche et Développement de
 # l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
@@ -47,6 +47,7 @@ EOF
 
 cat >expected <<EOF
 HOA: v1
+name: "3->1"
 States: 4
 Start: 0
 AP: 1 "c"
@@ -68,7 +69,7 @@ State: 3
 --END--
 EOF
 
-run 0 autfilt -H --remove-ap=a,b automaton >out
+run 0 autfilt -H --remove-ap=a,b --name='%X->%x' automaton >out
 cat out
 diff out expected