diff --git a/cartographer/mapping/internal/2d/pose_graph_2d.cc b/cartographer/mapping/internal/2d/pose_graph_2d.cc
index 4e4c141..b812dd1 100644
--- a/cartographer/mapping/internal/2d/pose_graph_2d.cc
+++ b/cartographer/mapping/internal/2d/pose_graph_2d.cc
@@ -42,6 +42,8 @@ namespace cartographer {
 namespace mapping {
 
 static auto* kWorkQueueDelayMetric = metrics::Gauge::Null();
+static auto* kConstraintsSameTrajectoryMetric = metrics::Gauge::Null();
+static auto* kConstraintsDifferentTrajectoryMetric = metrics::Gauge::Null();
 
 PoseGraph2D::PoseGraph2D(
     const proto::PoseGraphOptions& options,
@@ -478,6 +480,25 @@ void PoseGraph2D::HandleWorkQueue(
         trimmers_.end());
 
     num_nodes_since_last_loop_closure_ = 0;
+
+    // Update the gauges that count the current number of constraints.
+    double inter_constraints_same_trajectory = 0;
+    double inter_constraints_different_trajectory = 0;
+    for (const auto& constraint : data_.constraints) {
+      if (constraint.tag ==
+          cartographer::mapping::PoseGraph::Constraint::INTRA_SUBMAP) {
+        continue;
+      }
+      if (constraint.node_id.trajectory_id ==
+          constraint.submap_id.trajectory_id) {
+        ++inter_constraints_same_trajectory;
+      } else {
+        ++inter_constraints_different_trajectory;
+      }
+    }
+    kConstraintsSameTrajectoryMetric->Set(inter_constraints_same_trajectory);
+    kConstraintsDifferentTrajectoryMetric->Set(
+        inter_constraints_different_trajectory);
   }
 
   DrainWorkQueue();
@@ -1205,6 +1226,13 @@ void PoseGraph2D::RegisterMetrics(metrics::FamilyFactory* family_factory) {
       "mapping_2d_pose_graph_work_queue_delay",
       "Age of the oldest entry in the work queue in seconds");
   kWorkQueueDelayMetric = latency->Add({});
+  auto* constraints = family_factory->NewGaugeFamily(
+      "mapping_2d_pose_graph_constraints",
+      "Current number of constraints in the pose graph");
+  kConstraintsDifferentTrajectoryMetric =
+      constraints->Add({{"tag", "inter_submap"}, {"trajectory", "different"}});
+  kConstraintsSameTrajectoryMetric =
+      constraints->Add({{"tag", "inter_submap"}, {"trajectory", "same"}});
 }
 
 }  // namespace mapping
diff --git a/cartographer/mapping/internal/3d/pose_graph_3d.cc b/cartographer/mapping/internal/3d/pose_graph_3d.cc
index 5a2842a..d79c186 100644
--- a/cartographer/mapping/internal/3d/pose_graph_3d.cc
+++ b/cartographer/mapping/internal/3d/pose_graph_3d.cc
@@ -40,6 +40,8 @@ namespace cartographer {
 namespace mapping {
 
 static auto* kWorkQueueDelayMetric = metrics::Gauge::Null();
+static auto* kConstraintsSameTrajectoryMetric = metrics::Gauge::Null();
+static auto* kConstraintsDifferentTrajectoryMetric = metrics::Gauge::Null();
 
 PoseGraph3D::PoseGraph3D(
     const proto::PoseGraphOptions& options,
@@ -472,6 +474,25 @@ void PoseGraph3D::HandleWorkQueue(
         trimmers_.end());
 
     num_nodes_since_last_loop_closure_ = 0;
+
+    // Update the gauges that count the current number of constraints.
+    double inter_constraints_same_trajectory = 0;
+    double inter_constraints_different_trajectory = 0;
+    for (const auto& constraint : data_.constraints) {
+      if (constraint.tag ==
+          cartographer::mapping::PoseGraph::Constraint::INTRA_SUBMAP) {
+        continue;
+      }
+      if (constraint.node_id.trajectory_id ==
+          constraint.submap_id.trajectory_id) {
+        ++inter_constraints_same_trajectory;
+      } else {
+        ++inter_constraints_different_trajectory;
+      }
+    }
+    kConstraintsSameTrajectoryMetric->Set(inter_constraints_same_trajectory);
+    kConstraintsDifferentTrajectoryMetric->Set(
+        inter_constraints_different_trajectory);
   }
 
   DrainWorkQueue();
@@ -1208,6 +1229,13 @@ void PoseGraph3D::RegisterMetrics(metrics::FamilyFactory* family_factory) {
       "mapping_3d_pose_graph_work_queue_delay",
       "Age of the oldest entry in the work queue in seconds");
   kWorkQueueDelayMetric = latency->Add({});
+  auto* constraints = family_factory->NewGaugeFamily(
+      "mapping_3d_pose_graph_constraints",
+      "Current number constraints in the pose graph");
+  kConstraintsDifferentTrajectoryMetric =
+      constraints->Add({{"tag", "inter_submap"}, {"trajectory", "different"}});
+  kConstraintsSameTrajectoryMetric =
+      constraints->Add({{"tag", "inter_submap"}, {"trajectory", "same"}});
 }
 
 }  // namespace mapping