diff --git a/src/calibre/ebooks/__init__.py b/src/calibre/ebooks/__init__.py
index bdbdca85c8..b308b092e9 100644
--- a/src/calibre/ebooks/__init__.py
+++ b/src/calibre/ebooks/__init__.py
@@ -133,7 +133,8 @@ def render_html(path_to_html, width=590, height=750, as_xhtml=True):
     from PyQt4.QtWebKit import QWebPage
     from PyQt4.Qt import QEventLoop, QPalette, Qt, QUrl, QSize
     from calibre.gui2 import is_ok_to_use_qt
-    if not is_ok_to_use_qt(): return None
+    if not is_ok_to_use_qt():
+        return None
     path_to_html = os.path.abspath(path_to_html)
     with CurrentDir(os.path.dirname(path_to_html)):
         page = QWebPage()
@@ -214,9 +215,9 @@ def calibre_cover(title, author_string, series_string=None,
         if cleanup:
             os.remove(font_path)
 
-UNIT_RE = re.compile(r'^(-*[0-9]*[.]?[0-9]*)\s*(%|em|ex|en|px|mm|cm|in|pt|pc)$')
+UNIT_RE = re.compile(r'^(-*[0-9]*[.]?[0-9]*)\s*(%|em|ex|en|px|mm|cm|in|pt|pc|rem)$')
 
-def unit_convert(value, base, font, dpi):
+def unit_convert(value, base, font, dpi, body_font_size=12):
     ' Return value in pts'
     if isinstance(value, (int, long, float)):
         return value
@@ -250,6 +251,8 @@ def unit_convert(value, base, font, dpi):
             result = value * 2.8346456693
         elif unit == 'cm':
             result = value * 28.346456693
+        elif unit == 'rem':
+            result = value * body_font_size
     return result
 
 def generate_masthead(title, output_path=None, width=600, height=60):
diff --git a/src/calibre/ebooks/oeb/stylizer.py b/src/calibre/ebooks/oeb/stylizer.py
index f9618099a4..fbb8fb1f49 100644
--- a/src/calibre/ebooks/oeb/stylizer.py
+++ b/src/calibre/ebooks/oeb/stylizer.py
@@ -210,6 +210,7 @@ class Stylizer(object):
         if self.profile is None:
             # Just in case the default profile is removed in the future :)
             self.profile = opts.output_profile
+        self.body_font_size = self.profile.fbase
         self.logger = oeb.logger
         item = oeb.manifest.hrefs[path]
         basename = os.path.basename(path)
@@ -630,7 +631,7 @@ class Style(object):
             base = self.width
         if not font and font != 0:
             font = self.fontSize
-        return unit_convert(value, base, font, self._profile.dpi)
+        return unit_convert(value, base, font, self._profile.dpi, body_font_size=self._stylizer.body_font_size)
 
     def pt_to_px(self, value):
         return (self._profile.dpi / 72.0) * value
diff --git a/src/calibre/ebooks/oeb/transforms/flatcss.py b/src/calibre/ebooks/oeb/transforms/flatcss.py
index 1b678a3fe5..eadcdff4d0 100644
--- a/src/calibre/ebooks/oeb/transforms/flatcss.py
+++ b/src/calibre/ebooks/oeb/transforms/flatcss.py
@@ -310,6 +310,8 @@ class CSSFlattener(object):
         except:
             font_size = self.sbase if self.sbase is not None else \
                 self.context.source.fbase
+        if tag == 'body' and isinstance(font_size, (int, float)):
+            stylizer.body_font_size = font_size
         if 'align' in node.attrib:
             if tag != 'img':
                 cssdict['text-align'] = node.attrib['align']