diff --git a/src/ess/powder/calibration.py b/src/ess/powder/calibration.py
index c110b8cc..b9c0a371 100644
--- a/src/ess/powder/calibration.py
+++ b/src/ess/powder/calibration.py
@@ -9,7 +9,14 @@
 import scipp as sc
 import scipp.constants
 
-from .types import CorrectedDetector, SampleRun
+from .types import (
+    DetectorLtotal,
+    DetectorTwoTheta,
+    ElasticCoordTransformGraph,
+    EmptyDetector,
+    RunType,
+    SampleRun,
+)
 
 
 class OutputCalibrationData(Mapping[int, sc.Variable]):
@@ -93,13 +100,34 @@ def to_cif_format(self) -> sc.DataArray:
         )
 
 
+def detector_two_theta(
+    detector: EmptyDetector[RunType],
+    graph: ElasticCoordTransformGraph[RunType],
+) -> DetectorTwoTheta[RunType]:
+    """Compute the scattering angle (two-theta) for each detector pixel.
+
+    Parameters
+    ----------
+    detector:
+        Data array with detector positions.
+    graph:
+        Coordinate transformation graph for elastic scattering.
+    """
+    return DetectorTwoTheta[RunType](
+        detector.transform_coords(
+            "two_theta", graph=graph, keep_intermediate=False
+        ).coords["two_theta"]
+    )
+
+
 def assemble_output_calibration(
-    data: CorrectedDetector[SampleRun],
+    ltotal: DetectorLtotal[SampleRun],
+    two_theta: DetectorTwoTheta[SampleRun],
 ) -> OutputCalibrationData:
     """Construct output calibration data from average pixel positions."""
     # Use nanmean because pixels without events have position=NaN.
-    average_l = sc.nanmean(data.coords["Ltotal"])
-    average_two_theta = sc.nanmean(data.coords["two_theta"])
+    average_l = sc.nanmean(ltotal)
+    average_two_theta = sc.nanmean(two_theta)
     difc = sc.to_unit(
         2
         * sc.constants.m_n
@@ -111,4 +139,4 @@ def assemble_output_calibration(
     return OutputCalibrationData({1: difc})
 
 
-providers = (assemble_output_calibration,)
+providers = (detector_two_theta, assemble_output_calibration)
diff --git a/src/ess/powder/types.py b/src/ess/powder/types.py
index db5b8065..5d34ffdd 100644
--- a/src/ess/powder/types.py
+++ b/src/ess/powder/types.py
@@ -36,6 +36,7 @@
 
 DetectorBankSizes = reduce_t.DetectorBankSizes
 
+DetectorLtotal = tof_t.DetectorLtotal
 TofDetector = tof_t.TofDetector
 TofMonitor = tof_t.TofMonitor
 PulseStrideOffset = tof_t.PulseStrideOffset
@@ -104,6 +105,10 @@ class WavelengthDetector(sciline.Scope[RunType, sc.DataArray], sc.DataArray):
 """Histogrammed intensity vs d-spacing."""
 
 
+class DetectorTwoTheta(sciline.Scope[RunType, sc.Variable], sc.Variable):
+    """Scattering angle (two-theta) for each detector pixel."""
+
+
 class ElasticCoordTransformGraph(sciline.Scope[RunType, dict], dict):
     """Graph for transforming coordinates in elastic scattering."""