diff --git a/qubesmanager/utils.py b/qubesmanager/utils.py
index 52c4bd6..e8d8ea5 100644
--- a/qubesmanager/utils.py
+++ b/qubesmanager/utils.py
@@ -30,8 +30,7 @@ import sys
 import quamash
 from qubesadmin import events
 
-from PyQt5 import QtWidgets, QtCore  # pylint: disable=import-error
-from PyQt5.QtGui import QIcon  # pylint: disable=import-error
+from PyQt5 import QtWidgets, QtCore, QtGui  # pylint: disable=import-error
 
 
 def _filter_internal(vm):
@@ -39,6 +38,36 @@ def _filter_internal(vm):
             and not vm.features.get('internal', False))
 
 
+class SizeSpinBox(QtWidgets.QSpinBox):
+    # pylint: disable=invalid-name, no-self-use
+    def __init__(self, *args, **kwargs):
+        super(SizeSpinBox, self).__init__(*args, **kwargs)
+
+        self.pattern = r'(\d+\.?\d?) ?(GB|MB)'
+        self.regex = re.compile(self.pattern)
+        self.validator = QtGui.QRegExpValidator(QtCore.QRegExp(
+            self.pattern), self)
+
+    def textFromValue(self, v: int) -> str:
+        if v > 1024:
+            return '{:.1f} GB'.format(v / 1024)
+
+        return '{} MB'.format(v)
+
+    def validate(self, text: str, pos: int):
+        return self.validator.validate(text, pos)
+
+    def valueFromText(self, text: str) -> int:
+        value, unit = self.regex.fullmatch(text.strip()).groups()
+
+        if unit == 'GB':
+            multiplier = 1024
+        else:
+            multiplier = 1
+
+        return int(float(value) * multiplier)
+
+
 def prepare_choice(widget, holder, propname, choice, default,
                    filter_function=None, *,
                    icon_getter=None, allow_internal=None, allow_default=False,
@@ -171,7 +200,7 @@ def prepare_label_choice(widget, holder, propname, default, *args, **kwargs):
                           sorted(app.labels.values(), key=lambda l: l.index),
                           default, *args,
                           icon_getter=(lambda label:
-                                       QIcon.fromTheme(label.icon)),
+                                       QtGui.QIcon.fromTheme(label.icon)),
                           **kwargs)
 
 
diff --git a/ui/settingsdlg.ui b/ui/settingsdlg.ui
index bb29417..f020ebd 100644
--- a/ui/settingsdlg.ui
+++ b/ui/settingsdlg.ui
@@ -110,16 +110,16 @@
              <number>15</number>
             </property>
             <item row="1" column="1">
-             <widget class="QSpinBox" name="root_resize">
+             <widget class="SizeSpinBox" name="root_resize">
               <property name="enabled">
                <bool>true</bool>
               </property>
+              <property name="toolTip">
+               <string>&lt;html&gt;&lt;head/&gt;&lt;body&gt;&lt;p&gt;Values displayed using the binary definition of gigabyte and megabyte, i.e. 1024&lt;span style=&quot; vertical-align:super;&quot;&gt;3&lt;/span&gt; and 1024&lt;span style=&quot; vertical-align:super;&quot;&gt;2 &lt;/span&gt;bytes respectively.&lt;/p&gt;&lt;/body&gt;&lt;/html&gt;</string>
+              </property>
               <property name="alignment">
                <set>Qt::AlignRight|Qt::AlignTrailing|Qt::AlignVCenter</set>
               </property>
-              <property name="suffix">
-               <string>MiB</string>
-              </property>
               <property name="maximum">
                <number>1048576</number>
               </property>
@@ -129,16 +129,16 @@
              </widget>
             </item>
             <item row="0" column="1">
-             <widget class="QSpinBox" name="max_priv_storage">
+             <widget class="SizeSpinBox" name="max_priv_storage">
               <property name="enabled">
                <bool>true</bool>
               </property>
+              <property name="toolTip">
+               <string>&lt;html&gt;&lt;head/&gt;&lt;body&gt;&lt;p&gt;Values displayed using the binary definition of gigabyte and megabyte, i.e. 1024&lt;span style=&quot; vertical-align:super;&quot;&gt;3&lt;/span&gt; and 1024&lt;span style=&quot; vertical-align:super;&quot;&gt;2 &lt;/span&gt;bytes respectively.&lt;/p&gt;&lt;/body&gt;&lt;/html&gt;</string>
+              </property>
               <property name="alignment">
                <set>Qt::AlignRight|Qt::AlignTrailing|Qt::AlignVCenter</set>
               </property>
-              <property name="suffix">
-               <string>MiB</string>
-              </property>
               <property name="minimum">
                <number>0</number>
               </property>
@@ -1556,6 +1556,13 @@ The qube must be running to disable seamless mode; this setting is not persisten
    </item>
   </layout>
  </widget>
+ <customwidgets>
+  <customwidget>
+   <class>SizeSpinBox</class>
+   <extends>QSpinBox</extends>
+   <header>qubesmanager/utils.h</header>
+  </customwidget>
+ </customwidgets>
  <tabstops>
   <tabstop>tabWidget</tabstop>
   <tabstop>vmname</tabstop>