diff --git a/src/calibre/ebooks/conversion/cli.py b/src/calibre/ebooks/conversion/cli.py
index 1c01f49635..163f24e313 100644
--- a/src/calibre/ebooks/conversion/cli.py
+++ b/src/calibre/ebooks/conversion/cli.py
@@ -137,7 +137,9 @@ def add_pipeline_options(parser, plumber):
                       'extra_css', 'smarten_punctuation',
                       'margin_top', 'margin_left', 'margin_right',
                       'margin_bottom', 'change_justification',
-                      'insert_blank_line', 'remove_paragraph_spacing','remove_paragraph_spacing_indent_size',
+                      'insert_blank_line', 'insert_blank_line_size',
+                      'remove_paragraph_spacing',
+                      'remove_paragraph_spacing_indent_size',
                       'asciiize',
                   ]
                   ),
diff --git a/src/calibre/ebooks/conversion/plumber.py b/src/calibre/ebooks/conversion/plumber.py
index 31f125dd88..3a82cd56ca 100644
--- a/src/calibre/ebooks/conversion/plumber.py
+++ b/src/calibre/ebooks/conversion/plumber.py
@@ -366,9 +366,9 @@ OptionRecommendation(name='remove_paragraph_spacing',
 
 OptionRecommendation(name='remove_paragraph_spacing_indent_size',
         recommended_value=1.5, level=OptionRecommendation.LOW,
-        help=_('When calibre removes inter paragraph spacing, it automatically '
+        help=_('When calibre removes blank lines between paragraphs, it automatically '
             'sets a paragraph indent, to ensure that paragraphs can be easily '
-            'distinguished. This option controls the width of that indent.')
+            'distinguished. This option controls the width of that indent (in em).')
         ),
 
 OptionRecommendation(name='prefer_metadata_cover',
@@ -384,6 +384,13 @@ OptionRecommendation(name='insert_blank_line',
             )
         ),
 
+OptionRecommendation(name='insert_blank_line_size',
+        recommended_value=0.5, level=OptionRecommendation.LOW,
+        help=_('Set the height of the inserted blank lines (in em).'
+            ' The height of the lines between paragraphs will be twice the value'
+            ' set here.')
+        ),
+
 OptionRecommendation(name='remove_first_image',
         recommended_value=False, level=OptionRecommendation.LOW,
         help=_('Remove the first image from the input ebook. Useful if the '
diff --git a/src/calibre/ebooks/oeb/transforms/flatcss.py b/src/calibre/ebooks/oeb/transforms/flatcss.py
index 368f5eb289..d006d8dd2d 100644
--- a/src/calibre/ebooks/oeb/transforms/flatcss.py
+++ b/src/calibre/ebooks/oeb/transforms/flatcss.py
@@ -318,7 +318,8 @@ class CSSFlattener(object):
                     for edge in ('top', 'bottom'):
                         cssdict['%s-%s'%(prop, edge)] = '0pt'
             if self.context.insert_blank_line:
-                cssdict['margin-top'] = cssdict['margin-bottom'] = '0.5em'
+                cssdict['margin-top'] = cssdict['margin-bottom'] = \
+                    '%fem'%self.context.insert_blank_line_size
             if self.context.remove_paragraph_spacing:
                 cssdict['text-indent'] =  "%1.1fem" % self.context.remove_paragraph_spacing_indent_size
 
diff --git a/src/calibre/gui2/convert/look_and_feel.py b/src/calibre/gui2/convert/look_and_feel.py
index 98b9cb8155..9b008c0d6d 100644
--- a/src/calibre/gui2/convert/look_and_feel.py
+++ b/src/calibre/gui2/convert/look_and_feel.py
@@ -24,7 +24,10 @@ class LookAndFeelWidget(Widget, Ui_Form):
                     'font_size_mapping', 'line_height', 'minimum_line_height',
                     'linearize_tables', 'smarten_punctuation',
                     'disable_font_rescaling', 'insert_blank_line',
-                    'remove_paragraph_spacing', 'remove_paragraph_spacing_indent_size','input_encoding',
+                    'remove_paragraph_spacing',
+                    'remove_paragraph_spacing_indent_size',
+                    'insert_blank_line_size',
+                    'input_encoding',
                     'asciiize', 'keep_ligatures']
                 )
         for val, text in [
diff --git a/src/calibre/gui2/convert/look_and_feel.ui b/src/calibre/gui2/convert/look_and_feel.ui
index 3dea1f66d7..0aa91e0f47 100644
--- a/src/calibre/gui2/convert/look_and_feel.ui
+++ b/src/calibre/gui2/convert/look_and_feel.ui
@@ -6,7 +6,7 @@
    <rect>
     <x>0</x>
     <y>0</y>
-    <width>600</width>
+    <width>642</width>
     <height>500</height>
    </rect>
   </property>
@@ -31,7 +31,7 @@
      </property>
     </widget>
    </item>
-   <item row="1" column="1" colspan="2">
+   <item row="1" column="1">
     <widget class="QDoubleSpinBox" name="opt_base_font_size">
      <property name="suffix">
       <string> pt</string>
@@ -97,6 +97,29 @@
      </item>
     </layout>
    </item>
+   <item row="3" column="0">
+    <widget class="QLabel" name="label_6">
+     <property name="text">
+      <string>Minimum &amp;line height:</string>
+     </property>
+     <property name="buddy">
+      <cstring>opt_minimum_line_height</cstring>
+     </property>
+    </widget>
+   </item>
+   <item row="3" column="1">
+    <widget class="QDoubleSpinBox" name="opt_minimum_line_height">
+     <property name="suffix">
+      <string> %</string>
+     </property>
+     <property name="decimals">
+      <number>1</number>
+     </property>
+     <property name="maximum">
+      <double>900.000000000000000</double>
+     </property>
+    </widget>
+   </item>
    <item row="4" column="0">
     <widget class="QLabel" name="label">
      <property name="text">
@@ -107,7 +130,7 @@
      </property>
     </widget>
    </item>
-   <item row="4" column="1" colspan="2">
+   <item row="4" column="1">
     <widget class="QDoubleSpinBox" name="opt_line_height">
      <property name="suffix">
       <string> pt</string>
@@ -127,6 +150,13 @@
      </property>
     </widget>
    </item>
+   <item row="5" column="1" colspan="2">
+    <widget class="EncodingComboBox" name="opt_input_encoding">
+     <property name="editable">
+      <bool>true</bool>
+     </property>
+    </widget>
+   </item>
    <item row="6" column="0" colspan="2">
     <widget class="QCheckBox" name="opt_remove_paragraph_spacing">
      <property name="text">
@@ -134,48 +164,58 @@
      </property>
     </widget>
    </item>
-   <item row="6" column="2" colspan="2">
-    <layout class="QHBoxLayout" name="horizontalLayout_2">
-     <item>
-      <widget class="QLabel" name="label_4">
-       <property name="text">
-        <string>Indent size:</string>
-       </property>
-       <property name="alignment">
-        <set>Qt::AlignRight|Qt::AlignTrailing|Qt::AlignVCenter</set>
-       </property>
-      </widget>
-     </item>
-     <item>
-      <widget class="QDoubleSpinBox" name="opt_remove_paragraph_spacing_indent_size">
-       <property name="toolTip">
-        <string>&lt;p&gt;When calibre removes inter paragraph spacing, it automatically sets a paragraph indent, to ensure that paragraphs can be easily distinguished. This option controls the width of that indent.</string>
-       </property>
-       <property name="suffix">
-        <string> em</string>
-       </property>
-       <property name="decimals">
-        <number>1</number>
-       </property>
-      </widget>
-     </item>
-    </layout>
-   </item>
-   <item row="7" column="0">
-    <widget class="QLabel" name="label_5">
+   <item row="7" column="0" colspan="2">
+    <widget class="QCheckBox" name="opt_insert_blank_line">
      <property name="text">
-      <string>Text justification:</string>
+      <string>Insert &amp;blank line between paragraphs</string>
+     </property>
+    </widget>
+   </item>
+   <item row="7" column="4">
+    <widget class="QDoubleSpinBox" name="opt_insert_blank_line_size">
+     <property name="suffix">
+      <string> em</string>
+     </property>
+     <property name="decimals">
+      <number>1</number>
      </property>
     </widget>
    </item>
    <item row="8" column="0">
+    <widget class="QLabel" name="label_5">
+     <property name="text">
+      <string>Text &amp;justification:</string>
+     </property>
+     <property name="buddy">
+      <cstring>opt_change_justification</cstring>
+     </property>
+    </widget>
+   </item>
+   <item row="8" column="2" colspan="3">
+    <widget class="QComboBox" name="opt_change_justification"/>
+   </item>
+   <item row="9" column="0">
     <widget class="QCheckBox" name="opt_linearize_tables">
      <property name="text">
       <string>&amp;Linearize tables</string>
      </property>
     </widget>
    </item>
-   <item row="11" column="0" colspan="4">
+   <item row="9" column="1" colspan="4">
+    <widget class="QCheckBox" name="opt_asciiize">
+     <property name="text">
+      <string>&amp;Transliterate unicode characters to ASCII</string>
+     </property>
+    </widget>
+   </item>
+   <item row="10" column="1" colspan="2">
+    <widget class="QCheckBox" name="opt_keep_ligatures">
+     <property name="text">
+      <string>Keep &amp;ligatures</string>
+     </property>
+    </widget>
+   </item>
+   <item row="12" column="0" colspan="5">
     <widget class="QGroupBox" name="groupBox">
      <property name="title">
       <string>Extra &amp;CSS</string>
@@ -187,27 +227,16 @@
      </layout>
     </widget>
    </item>
-   <item row="7" column="2" colspan="2">
-    <widget class="QComboBox" name="opt_change_justification"/>
-   </item>
-   <item row="8" column="1" colspan="3">
-    <widget class="QCheckBox" name="opt_asciiize">
-     <property name="text">
-      <string>&amp;Transliterate unicode characters to ASCII</string>
+   <item row="6" column="4">
+    <widget class="QDoubleSpinBox" name="opt_remove_paragraph_spacing_indent_size">
+     <property name="toolTip">
+      <string>&lt;p&gt;When calibre removes inter paragraph spacing, it automatically sets a paragraph indent, to ensure that paragraphs can be easily distinguished. This option controls the width of that indent.</string>
      </property>
-    </widget>
-   </item>
-   <item row="9" column="0">
-    <widget class="QCheckBox" name="opt_insert_blank_line">
-     <property name="text">
-      <string>Insert &amp;blank line</string>
+     <property name="suffix">
+      <string> em</string>
      </property>
-    </widget>
-   </item>
-   <item row="9" column="1" colspan="2">
-    <widget class="QCheckBox" name="opt_keep_ligatures">
-     <property name="text">
-      <string>Keep &amp;ligatures</string>
+     <property name="decimals">
+      <number>1</number>
      </property>
     </widget>
    </item>
@@ -218,33 +247,29 @@
      </property>
     </widget>
    </item>
-   <item row="3" column="0">
-    <widget class="QLabel" name="label_6">
+   <item row="6" column="3">
+    <widget class="QLabel" name="label_4">
      <property name="text">
-      <string>Minimum &amp;line height:</string>
+      <string>&amp;Indent size:</string>
+     </property>
+     <property name="alignment">
+      <set>Qt::AlignRight|Qt::AlignTrailing|Qt::AlignVCenter</set>
      </property>
      <property name="buddy">
-      <cstring>opt_minimum_line_height</cstring>
+      <cstring>opt_remove_paragraph_spacing_indent_size</cstring>
      </property>
     </widget>
    </item>
-   <item row="3" column="1" colspan="2">
-    <widget class="QDoubleSpinBox" name="opt_minimum_line_height">
-     <property name="suffix">
-      <string> %</string>
+   <item row="7" column="3">
+    <widget class="QLabel" name="label_7">
+     <property name="text">
+      <string>&amp;Line size:</string>
      </property>
-     <property name="decimals">
-      <number>1</number>
+     <property name="alignment">
+      <set>Qt::AlignRight|Qt::AlignTrailing|Qt::AlignVCenter</set>
      </property>
-     <property name="maximum">
-      <double>900.000000000000000</double>
-     </property>
-    </widget>
-   </item>
-   <item row="5" column="1" colspan="3">
-    <widget class="EncodingComboBox" name="opt_input_encoding">
-     <property name="editable">
-      <bool>true</bool>
+     <property name="buddy">
+      <cstring>opt_insert_blank_line_size</cstring>
      </property>
     </widget>
    </item>