diff --git a/src/elli/result.py b/src/elli/result.py
index 17bc67fa..bfdb65c6 100644
--- a/src/elli/result.py
+++ b/src/elli/result.py
@@ -298,7 +298,7 @@ def T(self) -> npt.NDArray:
         r"""Returns the absolute transmittance for unpolarized light.
 
         .. math::
-            T = T_{pp} / T_{ss}
+            T = (T_{pp} / T_{ss}) / 2
         """
         return (self.T_matrix[:, 0, 0] + self.T_matrix[:, 1, 1]) / 2