diff --git a/src/mon/OSDMonitor.cc b/src/mon/OSDMonitor.cc
index 7bf8a2d76b0cc4..4fbeed9a4abcdd 100644
--- a/src/mon/OSDMonitor.cc
+++ b/src/mon/OSDMonitor.cc
@@ -7784,22 +7784,56 @@ int OSDMonitor::get_crush_rule(const string &rule_name,
   return 0;
 }
 
-int OSDMonitor::check_pg_num(int64_t pool, int pg_num, int size, ostream *ss)
+int OSDMonitor::check_pg_num(int64_t pool, int pg_num, int size, int crush_rule, ostream *ss)
 {
   auto max_pgs_per_osd = g_conf().get_val<uint64_t>("mon_max_pg_per_osd");
-  auto num_osds = std::max(osdmap.get_num_in_osds(), 3u);   // assume min cluster size 3
-  auto max_pgs = max_pgs_per_osd * num_osds;
   uint64_t projected = 0;
+  unsigned osd_num = 0;
+  // assume min cluster size 3
+  auto num_osds = std::max(osdmap.get_num_in_osds(), 3u);
   if (pool < 0) {
+    // a new pool
     projected += pg_num * size;
   }
-  for (const auto& i : osdmap.get_pools()) {
-    if (i.first == pool) {
+  if (mapping.get_epoch() >= osdmap.get_epoch()) {
+    set<int> roots;
+    CrushWrapper newcrush = _get_pending_crush();
+    newcrush.find_takes_by_rule(crush_rule, &roots);
+    int max_osd = osdmap.get_max_osd();
+    for (auto root : roots) {
+      const char *rootname = newcrush.get_item_name(root);
+      set<int> osd_ids;
+      newcrush.get_leaves(rootname, &osd_ids);
+      unsigned out_osd = 0;
+      for (auto id : osd_ids) {
+	if (id > max_osd) { 
+	  out_osd++;
+	  continue;
+	}
+	projected += mapping.get_osd_acting_pgs(id).size();
+      }
+      osd_num += osd_ids.size() - out_osd;
+    }
+    if (pool >= 0) {   
+      // update an existing pool's pg num
+      const auto& pg_info = osdmap.get_pools().at(pool);    
+      // already counted the pgs of this `pool` by iterating crush map, so 
+      // remove them using adding the specified pg num
       projected += pg_num * size;
-    } else {
-      projected += i.second.get_pg_num_target() * i.second.get_size();
+      projected -= pg_info.get_pg_num_target() * pg_info.get_size();
+    }
+    num_osds = std::max(osd_num, 3u);  // assume min cluster size 3
+  } else {
+    // use pg_num target for evaluating the projected pg num
+    for (const auto& [pool_id, pool_info] : osdmap.get_pools()) {
+      if (pool_id == pool) {
+	projected += pg_num * size;
+      } else {
+	projected += pool_info.get_pg_num_target() * pool_info.get_size();
+      }
     }
   }
+  auto max_pgs = max_pgs_per_osd * num_osds;
   if (projected > max_pgs) {
     if (pool >= 0) {
       *ss << "pool id " << pool;
@@ -7895,13 +7929,7 @@ int OSDMonitor::prepare_new_pool(string& name,
              << duration << dendl;
   }
   unsigned size, min_size;
-  r = prepare_pool_size(pool_type, erasure_code_profile, repl_size,
-                        &size, &min_size, ss);
-  if (r) {
-    dout(10) << "prepare_pool_size returns " << r << dendl;
-    return r;
-  }
-  r = check_pg_num(-1, pg_num, size, ss);
+  r = check_pg_num(-1, pg_num, size, crush_rule, ss);
   if (r) {
     dout(10) << "check_pg_num returns " << r << dendl;
     return r;
@@ -8168,7 +8196,7 @@ int OSDMonitor::prepare_command_pool_set(const cmdmap_t& cmdmap,
     if (!osdmap.crush->check_crush_rule(p.get_crush_rule(), p.type, n, ss)) {
       return -EINVAL;
     }
-    int r = check_pg_num(pool, p.get_pg_num(), n, &ss);
+    int r = check_pg_num(pool, p.get_pg_num(), n, p.get_crush_rule(), &ss);
     if (r < 0) {
       return r;
     }
@@ -8274,7 +8302,7 @@ int OSDMonitor::prepare_command_pool_set(const cmdmap_t& cmdmap,
       return -ERANGE;
     }
     if (n > (int)p.get_pg_num_target()) {
-      int r = check_pg_num(pool, n, p.get_size(), &ss);
+      int r = check_pg_num(pool, n, p.get_size(), p.get_crush_rule(), &ss);
       if (r) {
 	return r;
       }
diff --git a/src/mon/OSDMonitor.h b/src/mon/OSDMonitor.h
index 255902169d9bd8..b0455fd3b51a4f 100644
--- a/src/mon/OSDMonitor.h
+++ b/src/mon/OSDMonitor.h
@@ -521,7 +521,7 @@ class OSDMonitor : public PaxosService,
 				const std::string &erasure_code_profile,
 				unsigned *stripe_width,
 				std::ostream *ss);
-  int check_pg_num(int64_t pool, int pg_num, int size, std::ostream* ss);
+  int check_pg_num(int64_t pool, int pg_num, int size, int crush_rule, std::ostream* ss);
   int prepare_new_pool(std::string& name,
 		       int crush_rule,
 		       const std::string &crush_rule_name,
diff --git a/src/osd/OSDMapMapping.h b/src/osd/OSDMapMapping.h
index 70258ff4e8d696..3357a61d74c718 100644
--- a/src/osd/OSDMapMapping.h
+++ b/src/osd/OSDMapMapping.h
@@ -321,7 +321,7 @@ class OSDMapMapping {
     }
   }
 
-  const mempool::osdmap_mapping::vector<pg_t>& get_osd_acting_pgs(unsigned osd) {
+  const mempool::osdmap_mapping::vector<pg_t>& get_osd_acting_pgs(unsigned osd) { 
     ceph_assert(osd < acting_rmap.size());
     return acting_rmap[osd];
   }