diff --git a/src/hyperion/external_interaction/callbacks/ispyb_callback_base.py b/src/hyperion/external_interaction/callbacks/ispyb_callback_base.py
index 42b2f50bf..b841f86c2 100644
--- a/src/hyperion/external_interaction/callbacks/ispyb_callback_base.py
+++ b/src/hyperion/external_interaction/callbacks/ispyb_callback_base.py
@@ -107,11 +107,13 @@ def _handle_ispyb_hardware_read(self, doc) -> Sequence[ScanDataInfo]:
             **doc["data"]["aperture_scatterguard-selected_aperture"]
         )
         beamsize = beam_size_from_aperture(aperture_size)
+        beamsize_x_mm = beamsize.x_um / 1000 if beamsize.x_um else None
+        beamsize_y_mm = beamsize.y_um / 1000 if beamsize.y_um else None
         hwscan_data_collection_info = DataCollectionInfo(
-            beamsize_at_samplex=beamsize.x_um,
-            beamsize_at_sampley=beamsize.y_um,
-            focal_spot_size_at_samplex=beamsize.x_um,
-            focal_spot_size_at_sampley=beamsize.y_um,
+            beamsize_at_samplex=beamsize_x_mm,
+            beamsize_at_sampley=beamsize_y_mm,
+            focal_spot_size_at_samplex=beamsize_x_mm,
+            focal_spot_size_at_sampley=beamsize_y_mm,
             undulator_gap1=doc["data"]["undulator-current_gap"],
             synchrotron_mode=synchrotron_mode.value,
             slitgap_horizontal=doc["data"]["s4_slit_gaps_xgap"],
diff --git a/tests/unit_tests/external_interaction/callbacks/rotation/test_ispyb_callback.py b/tests/unit_tests/external_interaction/callbacks/rotation/test_ispyb_callback.py
index 9a47f2c3c..86e55c83b 100644
--- a/tests/unit_tests/external_interaction/callbacks/rotation/test_ispyb_callback.py
+++ b/tests/unit_tests/external_interaction/callbacks/rotation/test_ispyb_callback.py
@@ -149,10 +149,10 @@ def test_hardware_read_events(
             "slitgapvertical": 0.2345,
             "synchrotronmode": "User",
             "undulatorgap1": 1.234,
-            "focal_spot_size_at_samplex": 50.0,
-            "focal_spot_size_at_sampley": 20.0,
-            "beamsize_at_samplex": 50.0,
-            "beamsize_at_sampley": 20.0,
+            "focal_spot_size_at_samplex": 0.05,
+            "focal_spot_size_at_sampley": 0.02,
+            "beamsize_at_samplex": 0.05,
+            "beamsize_at_sampley": 0.02,
             "comments": "Sample position: (10.0, 20.0, 30.0) test Aperture: Medium",
         },
     )
@@ -327,10 +327,10 @@ def test_comment_correct_after_hardware_read(
             "slitgapvertical": 0.2345,
             "synchrotronmode": "User",
             "undulatorgap1": 1.234,
-            "focal_spot_size_at_samplex": 50.0,
-            "focal_spot_size_at_sampley": 20.0,
-            "beamsize_at_samplex": 50.0,
-            "beamsize_at_sampley": 20.0,
+            "focal_spot_size_at_samplex": 0.05,
+            "focal_spot_size_at_sampley": 0.02,
+            "beamsize_at_samplex": 0.05,
+            "beamsize_at_sampley": 0.02,
             "comments": "Sample position: (10.0, 20.0, 30.0) a lovely unit test Aperture: Medium",
         },
     )
diff --git a/tests/unit_tests/external_interaction/callbacks/xray_centre/test_ispyb_callback.py b/tests/unit_tests/external_interaction/callbacks/xray_centre/test_ispyb_callback.py
index d46c73c9e..ec9bd51c1 100644
--- a/tests/unit_tests/external_interaction/callbacks/xray_centre/test_ispyb_callback.py
+++ b/tests/unit_tests/external_interaction/callbacks/xray_centre/test_ispyb_callback.py
@@ -100,10 +100,10 @@ def test_hardware_read_event_3d(self, mock_ispyb_conn):
                 "slitgapvertical": 0.2345,
                 "synchrotronmode": "User",
                 "undulatorgap1": 1.234,
-                "focal_spot_size_at_samplex": 50.0,
-                "focal_spot_size_at_sampley": 20.0,
-                "beamsize_at_samplex": 50.0,
-                "beamsize_at_sampley": 20.0,
+                "focal_spot_size_at_samplex": 0.05,
+                "focal_spot_size_at_sampley": 0.02,
+                "beamsize_at_samplex": 0.05,
+                "beamsize_at_sampley": 0.02,
             },
         )
         assert_upsert_call_with(
@@ -116,10 +116,10 @@ def test_hardware_read_event_3d(self, mock_ispyb_conn):
                 "slitgapvertical": 0.2345,
                 "synchrotronmode": "User",
                 "undulatorgap1": 1.234,
-                "focal_spot_size_at_samplex": 50.0,
-                "focal_spot_size_at_sampley": 20.0,
-                "beamsize_at_samplex": 50.0,
-                "beamsize_at_sampley": 20.0,
+                "focal_spot_size_at_samplex": 0.05,
+                "focal_spot_size_at_sampley": 0.02,
+                "beamsize_at_samplex": 0.05,
+                "beamsize_at_sampley": 0.02,
             },
         )