diff --git a/src/calibre/gui2/viewer/web_view.py b/src/calibre/gui2/viewer/web_view.py
index 5a0b0de1ca..30e0f33574 100644
--- a/src/calibre/gui2/viewer/web_view.py
+++ b/src/calibre/gui2/viewer/web_view.py
@@ -9,8 +9,8 @@ import sys
 from itertools import count
 
 from PyQt5.Qt import (
-    QApplication, QBuffer, QByteArray, QFontDatabase, QHBoxLayout, QSize, Qt, QTimer,
-    QUrl, QWidget, pyqtSignal
+    QApplication, QBuffer, QByteArray, QFontDatabase, QFontInfo, QHBoxLayout, QSize,
+    Qt, QTimer, QUrl, QWidget, pyqtSignal
 )
 from PyQt5.QtWebEngineCore import QWebEngineUrlSchemeHandler
 from PyQt5.QtWebEngineWidgets import (
@@ -427,9 +427,10 @@ class WebView(RestartingWebEngineView):
 
     def on_bridge_ready(self):
         f = QApplication.instance().font()
+        fi = QFontInfo(f)
         self.bridge.create_view(
             vprefs['session_data'], QFontDatabase().families(), field_metadata.all_metadata(),
-            f.family(), f.pointSize())
+            f.family(), '{}px'.format(fi.pixelSize()))
         for func, args in iteritems(self.pending_bridge_ready_actions):
             getattr(self.bridge, func)(*args)
 
diff --git a/src/pyj/viewer-main.pyj b/src/pyj/viewer-main.pyj
index 101453c963..b63e8a1908 100644
--- a/src/pyj/viewer-main.pyj
+++ b/src/pyj/viewer-main.pyj
@@ -188,12 +188,12 @@ def create_session_data(prefs):
 
 
 @from_python
-def create_view(prefs, all_font_families, field_metadata, ui_font_family, ui_font_sz_in_pts):
+def create_view(prefs, all_font_families, field_metadata, ui_font_family, ui_font_sz):
     nonlocal view
     runtime.all_font_families = all_font_families
     library_data.field_metadata = field_metadata
     document.documentElement.style.fontFamily = f'"{ui_font_family}", sans-serif'
-    document.documentElement.style.fontSize = f'{ui_font_sz_in_pts}pt'
+    document.documentElement.style.fontSize = ui_font_sz
     if view is None:
         create_session_data(prefs)
         view = View(document.getElementById('view'))