diff --git a/CHANGES b/CHANGES
index 20ac78fa6..f6bbce98b 100644
--- a/CHANGES
+++ b/CHANGES
@@ -14,6 +14,7 @@ Features added
 --------------
 
 * LaTeX: Make the ``toplevel_sectioning`` setting optional in LaTeX theme
+* LaTeX: Allow to override papersize and pointsize from LaTeX themes
 
 Bugs fixed
 ----------
diff --git a/sphinx/builders/latex/__init__.py b/sphinx/builders/latex/__init__.py
index 390a5d9c7..cd099943c 100644
--- a/sphinx/builders/latex/__init__.py
+++ b/sphinx/builders/latex/__init__.py
@@ -314,6 +314,8 @@ class LaTeXBuilder(Builder):
         self.context['title'] = title
         self.context['author'] = author
         self.context['docclass'] = theme.docclass
+        self.context['papersize'] = theme.papersize
+        self.context['pointsize'] = theme.pointsize
         self.context['wrapperclass'] = theme.wrapperclass
 
     def assemble_doctree(self, indexfile: str, toctree_only: bool, appendices: List[str]) -> nodes.document:  # NOQA
diff --git a/sphinx/builders/latex/constants.py b/sphinx/builders/latex/constants.py
index 9a89036bf..7146079ff 100644
--- a/sphinx/builders/latex/constants.py
+++ b/sphinx/builders/latex/constants.py
@@ -69,8 +69,8 @@ LUALATEX_DEFAULT_FONTPKG = XELATEX_DEFAULT_FONTPKG
 
 DEFAULT_SETTINGS = {
     'latex_engine':    'pdflatex',
-    'papersize':       'letterpaper',
-    'pointsize':       '10pt',
+    'papersize':       '',
+    'pointsize':       '',
     'pxunit':          '.75bp',
     'classoptions':    '',
     'extraclassoptions': '',
diff --git a/sphinx/builders/latex/theming.py b/sphinx/builders/latex/theming.py
index 4d5742ef6..1a4f48360 100644
--- a/sphinx/builders/latex/theming.py
+++ b/sphinx/builders/latex/theming.py
@@ -24,12 +24,23 @@ logger = logging.getLogger(__name__)
 class Theme:
     """A set of LaTeX configurations."""
 
+    LATEX_ELEMENTS_KEYS = ['papersize', 'pointsize']
+
     def __init__(self, name: str) -> None:
         self.name = name
         self.docclass = name
         self.wrapperclass = name
+        self.papersize = 'letterpaper'
+        self.pointsize = '10pt'
         self.toplevel_sectioning = 'chapter'
 
+    def update(self, config: Config) -> None:
+        """Override theme settings by user's configuration."""
+        for key in self.LATEX_ELEMENTS_KEYS:
+            if config.latex_elements.get(key):
+                value = config.latex_elements[key]
+                setattr(self, key, value)
+
 
 class BuiltInTheme(Theme):
     """A built-in LaTeX theme."""
@@ -59,7 +70,7 @@ class UserTheme(Theme):
     """A user defined LaTeX theme."""
 
     REQUIRED_CONFIG_KEYS = ['docclass', 'wrapperclass']
-    OPTIONAL_CONFIG_KEYS = ['toplevel_sectioning']
+    OPTIONAL_CONFIG_KEYS = ['papersize', 'pointsize', 'toplevel_sectioning']
 
     def __init__(self, name: str, filename: str) -> None:
         super().__init__(name)
@@ -89,6 +100,7 @@ class ThemeFactory:
     def __init__(self, app: Sphinx) -> None:
         self.themes = {}  # type: Dict[str, Theme]
         self.theme_paths = [path.join(app.srcdir, p) for p in app.config.latex_theme_path]
+        self.config = app.config
         self.load_builtin_themes(app.config)
 
     def load_builtin_themes(self, config: Config) -> None:
@@ -99,13 +111,14 @@ class ThemeFactory:
     def get(self, name: str) -> Theme:
         """Get a theme for given *name*."""
         if name in self.themes:
-            return self.themes[name]
+            theme = self.themes[name]
         else:
             theme = self.find_user_theme(name)
-            if theme:
-                return theme
-            else:
-                return Theme(name)
+            if not theme:
+                theme = Theme(name)
+
+        theme.update(self.config)
+        return theme
 
     def find_user_theme(self, name: str) -> Theme:
         """Find a theme named as *name* from latex_theme_path."""
diff --git a/tests/roots/test-latex-theme/theme/custom/theme.conf b/tests/roots/test-latex-theme/theme/custom/theme.conf
index 8961fac75..ad8df262f 100644
--- a/tests/roots/test-latex-theme/theme/custom/theme.conf
+++ b/tests/roots/test-latex-theme/theme/custom/theme.conf
@@ -1,4 +1,6 @@
 [theme]
 docclass = book
 wrapperclass = sphinxbook
+papersize = a4paper
+pointsize = 12pt
 toplevel_sectioning = chapter
diff --git a/tests/test_build_latex.py b/tests/test_build_latex.py
index 61020b861..ba70debc2 100644
--- a/tests/test_build_latex.py
+++ b/tests/test_build_latex.py
@@ -221,7 +221,18 @@ def test_latex_theme(app, status, warning):
     result = (app.outdir / 'python.tex').read_text(encoding='utf8')
     print(result)
     assert r'\def\sphinxdocclass{book}' in result
-    assert r'\documentclass[letterpaper,10pt,english]{sphinxbook}' in result
+    assert r'\documentclass[a4paper,12pt,english]{sphinxbook}' in result
+
+
+@pytest.mark.sphinx('latex', testroot='latex-theme',
+                    confoverrides={'latex_elements': {'papersize': 'b5paper',
+                                                      'pointsize': '9pt'}})
+def test_latex_theme_papersize(app, status, warning):
+    app.builder.build_all()
+    result = (app.outdir / 'python.tex').read_text(encoding='utf8')
+    print(result)
+    assert r'\def\sphinxdocclass{book}' in result
+    assert r'\documentclass[b5paper,9pt,english]{sphinxbook}' in result
 
 
 @pytest.mark.sphinx('latex', testroot='basic', confoverrides={'language': 'zh'})