diff --git a/improver/regrid/grid.py b/improver/regrid/grid.py
index 81bd7b7f77..5a2ed9d28d 100644
--- a/improver/regrid/grid.py
+++ b/improver/regrid/grid.py
@@ -66,8 +66,8 @@ def calculate_input_grid_spacing(cube_in: Cube) -> Tuple[float, float]:
         raise ValueError("Input grid is not on a latitude/longitude system")
 
     # calculate grid spacing
-    lon_spacing = calculate_grid_spacing(cube_in, "degree", axis="x", rtol=7.0e-5)
-    lat_spacing = calculate_grid_spacing(cube_in, "degree", axis="y", rtol=7.0e-5)
+    lon_spacing = calculate_grid_spacing(cube_in, "degree", axis="x", rtol=3.0e-5)
+    lat_spacing = calculate_grid_spacing(cube_in, "degree", axis="y", rtol=3.0e-5)
 
     if lon_spacing < 0 or lat_spacing < 0:
         raise ValueError("Input grid coordinates are not ascending.")
diff --git a/improver/utilities/spatial.py b/improver/utilities/spatial.py
index c960976858..81f1b597c8 100644
--- a/improver/utilities/spatial.py
+++ b/improver/utilities/spatial.py
@@ -77,7 +77,7 @@ def check_if_grid_is_equal_area(
 
 
 def calculate_grid_spacing(
-    cube: Cube, units: Union[Unit, str], axis: str = "x", rtol: float = 1.0e-6
+    cube: Cube, units: Union[Unit, str], axis: str = "x", rtol: float = 1.0e-5
 ) -> float:
     """
     Returns the grid spacing of a given spatial axis
diff --git a/improver_tests/utilities/test_spatial.py b/improver_tests/utilities/test_spatial.py
index d27da93a14..de7c18e25f 100644
--- a/improver_tests/utilities/test_spatial.py
+++ b/improver_tests/utilities/test_spatial.py
@@ -228,7 +228,7 @@ def setUp(self):
             10.0,
             20.00001,
         ]
-        self.longitude_points_2 = [
+        self.longitude_points_thirds = [
             160.0,
             160.33333,
             160.66667,
@@ -237,8 +237,8 @@ def setUp(self):
         ]
         self.rtol = 1.0e-5
         self.expected = 10.0
-        self.expected_2 = 0.33333
-        self.rtol_2 = 3.0e-5
+        self.expected_thirds = 0.33333
+        self.rtol_thirds = 3.0e-5
 
     def test_lat_lon_equal_spacing(self):
         """Test grid spacing outputs with lat-lon grid with tolerance"""
@@ -262,18 +262,22 @@ def test_lat_lon_not_equal_spacing(self):
         with self.assertRaisesRegex(ValueError, msg):
             calculate_grid_spacing(self.lat_lon_cube, "degrees", rtol=self.rtol)
 
-    def test_lat_lon_equal_spacing_recurring_decimal_spacing(self):
-        """Test grid spacing outputs with lat-lon grid with tolerance"""
-        self.lat_lon_cube.coord("longitude").points = self.longitude_points_2
+    def test_lat_lon_equal_spacing_recurring_decimal_spacing_fails(self):
+        """Test grid spacing with lat-lon grid with with 1/3 degree 
+        intervals with tolerance of 1.0e-5"""
+        self.lat_lon_cube.coord("longitude").points = self.longitude_points_thirds
         msg = "Coordinate longitude points are not equally spaced"
         with self.assertRaisesRegex(ValueError, msg):
             calculate_grid_spacing(self.lat_lon_cube, "degrees", rtol=self.rtol)
 
     def test_lat_lon_equal_spacing_recurring_decimal_spacing_2(self):
-        """Test grid spacing outputs with lat-lon grid with tolerance 3.0e-5"""
-        self.lat_lon_cube.coord("longitude").points = self.longitude_points_2
-        result = calculate_grid_spacing(self.lat_lon_cube, "degrees", rtol=self.rtol_2)
-        self.assertAlmostEqual(result, self.expected_2, places=5)
+        """Test grid spacing outputs with lat-lon grid with 1/3 degree
+        intervals with tolerance of 3.0e-5"""
+        self.lat_lon_cube.coord("longitude").points = self.longitude_points_thirds
+        result = calculate_grid_spacing(
+            self.lat_lon_cube, "degrees", rtol=self.rtol_thirds
+        )
+        self.assertAlmostEqual(result, self.expected_thirds, places=5)
 
 
 class Test_convert_distance_into_number_of_grid_cells(IrisTest):