diff --git a/nonos/api/analysis.py b/nonos/api/analysis.py
index d8cc67e8..cb225930 100644
--- a/nonos/api/analysis.py
+++ b/nonos/api/analysis.py
@@ -1652,3 +1652,12 @@ def items(self) -> ItemsView[str, "GasField"]:
         items of the dict
         """
         return self.dict.items()
+
+    @property
+    def nfields(self) -> int:
+        """
+        Returns
+        =======
+        The number of fields in the GasDataSet
+        """
+        return len(self.dict)
diff --git a/tests/test_load_data.py b/tests/test_load_data.py
index 51868089..df3d19d7 100644
--- a/tests/test_load_data.py
+++ b/tests/test_load_data.py
@@ -20,13 +20,13 @@ def test_roundtrip_simple(test_data_dir, tmp_path):
 
     os.chdir(tmp_path / "mydir")
     ds = GasDataSet(500)
-    assert len(list(ds.keys())) == 7
+    assert ds.nfields == 7
 
     gf = ds["RHO"].azimuthal_average()
 
     gf.save()
     dsnpy = GasDataSet.from_npy(500, operation="azimuthal_average")
-    assert len(list(dsnpy.keys())) == 1
+    assert dsnpy.nfields == 1
 
 
 def test_roundtrip_other_dir(test_data_dir, tmp_path):
@@ -34,7 +34,7 @@ def test_roundtrip_other_dir(test_data_dir, tmp_path):
     gf = GasDataSet(500)["RHO"].azimuthal_average()
     gf.save(tmp_path)
     dsnpy = GasDataSet.from_npy(500, operation="azimuthal_average", directory=tmp_path)
-    assert len(list(dsnpy.keys())) == 1
+    assert dsnpy.nfields == 1
 
 
 def test_api_vtk_by_name(test_data_dir):
@@ -64,7 +64,7 @@ def test_api_fluid_fargo3d(test_data_dir):
     on = 5
 
     ds = GasDataSet(on, fluid="dust2")
-    assert len(list(ds.keys())) == 1
+    assert ds.nfields == 1
 
     with pytest.raises(
         FileNotFoundError,