diff --git a/network-area-diagram/src/main/java/com/powsybl/nad/build/iidm/VoltageLevelFilter.java b/network-area-diagram/src/main/java/com/powsybl/nad/build/iidm/VoltageLevelFilter.java
index ff6bc2067..5d405742e 100644
--- a/network-area-diagram/src/main/java/com/powsybl/nad/build/iidm/VoltageLevelFilter.java
+++ b/network-area-diagram/src/main/java/com/powsybl/nad/build/iidm/VoltageLevelFilter.java
@@ -27,6 +27,10 @@ public VoltageLevelFilter(Set<VoltageLevel> voltageLevels) {
         this.voltageLevels = voltageLevels;
     }
 
+    public int getNbVoltageLevels() {
+        return voltageLevels.size();
+    }
+
     private Set<VoltageLevel> getVoltageLevels() {
         return voltageLevels;
     }
diff --git a/network-area-diagram/src/test/java/com/powsybl/nad/layout/LayoutWithInitialPositionsTest.java b/network-area-diagram/src/test/java/com/powsybl/nad/layout/LayoutWithInitialPositionsTest.java
index 0aa61e6ec..d76d89530 100644
--- a/network-area-diagram/src/test/java/com/powsybl/nad/layout/LayoutWithInitialPositionsTest.java
+++ b/network-area-diagram/src/test/java/com/powsybl/nad/layout/LayoutWithInitialPositionsTest.java
@@ -59,6 +59,16 @@ public void testDiamond() {
         checkLayoutWithInitialPositions(LayoutNetworkFactory.createDiamond());
     }
 
+    @Test
+    public void testNbVoltageLevels() {
+        Network network = LayoutNetworkFactory.createDiamond();
+
+        assertEquals(1, VoltageLevelFilter.createVoltageLevelDepthFilter(network, "A 400", 0).getNbVoltageLevels());
+        assertEquals(4, VoltageLevelFilter.createVoltageLevelDepthFilter(network, "A 400", 3).getNbVoltageLevels());
+        assertEquals(7, VoltageLevelFilter.createVoltageLevelDepthFilter(network, "A 400", 5).getNbVoltageLevels());
+        assertEquals(1, VoltageLevelFilter.createVoltageLevelDepthFilter(network, "A 400", 0).getNbVoltageLevels());
+    }
+
     private void checkLayoutWithInitialPositions(Network network) {
         Predicate<VoltageLevel> filter = vl -> vl.getNominalV() >= 100;