diff --git a/package/AUTHORS b/package/AUTHORS
index ed82321a9e..c8ba87c062 100644
--- a/package/AUTHORS
+++ b/package/AUTHORS
@@ -284,6 +284,7 @@ Chronological list of authors
   - Sai Udayagiri
   - Apoorva Verma
   - Aryaman Chaudhri
+  - Francesco Siciliani
 
 External code
 -------------
diff --git a/package/CHANGELOG b/package/CHANGELOG
index c043f683f0..b106b09dc3 100644
--- a/package/CHANGELOG
+++ b/package/CHANGELOG
@@ -18,11 +18,13 @@ The rules for this file:
          spyke7, talagayev, tanii1125, BradyAJohnston, hejamu, jeremyleung521,
          harshitgajjela-droid, kunjsinha, aygarwal, jauy123, Dreamstick9,
          ollyfutur, Amarendra22, charity-g, ParthUppal523, apoorva-01, RMeli,
-         raulloiscuns, Aryaman-Chaudhri
+         raulloiscuns, Aryaman-Chaudhri, sici17
 
  * 2.11.0
 
 Fixes
+ * Mass (u) has been added to MDAnalysis base units and clarified that physical
+   constants use CODATA 2010 values (Issue #3944, PR #5439)
  * Added `.gitattributes` to enforce LF (\n) as line endings and renormalized
    existing files to conform (Issue #5315, PR #5446)
  * `AtomGroup.rotate()` and the `rotateby` trajectory transformation now
diff --git a/package/MDAnalysis/units.py b/package/MDAnalysis/units.py
index d52e46d86c..70b8a226bf 100644
--- a/package/MDAnalysis/units.py
+++ b/package/MDAnalysis/units.py
@@ -47,8 +47,15 @@
    charge       :math:`e`      :math:`1.602176565 \times 10^{-19}` As
    force        kJ/(mol·Å)     :math:`1.66053892103219 \times 10^{-11}` J/m
    speed        Å/ps           :math:`100` m/s
+   mass         u              :math:`1.66053892103219 \times 10^{-27}` kg
    =========== ============== ===============================================
 
+MDAnalysis currently uses the NIST `CODATA 2010`_ values for physical constants.
+
+.. _`CODATA 2010`: 
+   https://physics.nist.gov/cuu/Constants/ArchiveASCII/allascii_2010.txt
+
+
 Implementation notes
 --------------------
 
@@ -407,6 +414,7 @@ def __getitem__(self, key):
     "charge": "e",
     "force": "kJ/(mol*A)",
     "speed": "A/ps",
+    "mass": "u",
 }
 
 
diff --git a/testsuite/MDAnalysisTests/utils/test_units.py b/testsuite/MDAnalysisTests/utils/test_units.py
index dad63d6b11..b37383f58a 100644
--- a/testsuite/MDAnalysisTests/utils/test_units.py
+++ b/testsuite/MDAnalysisTests/utils/test_units.py
@@ -181,6 +181,7 @@ def ref():
             "charge": "e",
             "force": "kJ/(mol*A)",
             "speed": "A/ps",
+            "mass": "u",
         }
         return ref