diff --git a/docs/gridspec.rst b/docs/gridspec.rst
index 2979bc1..3cfda6d 100644
--- a/docs/gridspec.rst
+++ b/docs/gridspec.rst
@@ -54,3 +54,37 @@ Example:
 .. code-block::
 
     {"grid": [1, 1]}
+
+
+
+HEALPix nested grid
+------------------------------------------
+
+The ``grid`` format is::
+
+    HXXX
+
+The ``ordering`` must be set to ``"nested"``. For details about this grid, see `here  <https://en.wikipedia.org/wiki/HEALPix>`_.
+
+Example:
+
+.. code-block::
+
+    {"grid": "H512", "ordering": "nested"}
+
+
+HEALPix ring grid
+------------------------------------------
+
+The ``grid`` format is::
+
+    HXXX
+
+The ``ordering`` can be omitted or set to ``"ring"``.  For details about this grid, see `here  <https://en.wikipedia.org/wiki/HEALPix>`_.
+
+Example:
+
+.. code-block::
+
+    {"grid": "H512", "ordering": "ring"}
+    {"grid": "H512"}
diff --git a/earthkit/regrid/sphinxext/generate_inventory_rst.py b/earthkit/regrid/sphinxext/generate_inventory_rst.py
index c606cb6..a4d31c0 100644
--- a/earthkit/regrid/sphinxext/generate_inventory_rst.py
+++ b/earthkit/regrid/sphinxext/generate_inventory_rst.py
@@ -23,7 +23,12 @@
 def to_str(gs):
     if isinstance(gs, str):
         return gs
-    return {"grid": gs["grid"]}
+
+    grid = gs["grid"]
+    if isinstance(grid, str) and grid.startswith("H"):
+        return {"grid": gs["grid"], "ordering": gs["ordering"]}
+    else:
+        return {"grid": gs["grid"]}
 
 
 def make_gs_block(source, target):