diff --git a/src/calibre/gui2/dialogs/trim_image.py b/src/calibre/gui2/dialogs/trim_image.py
index 0837b6629c..d9dea2db69 100644
--- a/src/calibre/gui2/dialogs/trim_image.py
+++ b/src/calibre/gui2/dialogs/trim_image.py
@@ -7,12 +7,18 @@ __copyright__ = '2013, Kovid Goyal <kovid at kovidgoyal.net>'
 import os
 import sys
 
-from qt.core import QCheckBox, QDialog, QDialogButtonBox, QFormLayout, QHBoxLayout, QIcon, QKeySequence, QLabel, QSize, QSpinBox, Qt, QToolBar, QVBoxLayout
+from qt.core import QCheckBox, QDialog, QDialogButtonBox, QFormLayout, QHBoxLayout, QIcon, QKeySequence, QLabel, QSize, QSpinBox, QDoubleSpinBox, Qt, QToolBar, QVBoxLayout
 
 from calibre.gui2 import gprefs
 from calibre.gui2.tweak_book.editor.canvas import Canvas
 
 
+def reduce_to_ratio(w, h, t):
+    h = min(h, w / t)
+    w = t * h
+    return int(w), int(h)
+
+
 class Region(QDialog):
 
     ignore_value_changes = False
@@ -30,6 +36,12 @@ class Region(QDialog):
         h.setRange(20, max_height), h.setSuffix(' px'), h.setValue(height)
         h.valueChanged.connect(self.value_changed)
         l.addRow(_('&Height:'), h)
+        self.ratio_input = r = QDoubleSpinBox(self)
+        r.setRange(0.0, 5.00), r.setDecimals(2), r.setValue(max_width/max_height), r.setToolTip('For example, use 0.75 for kindle devices.')
+        self.m_width = max_width
+        self.m_height = max_height
+        r.valueChanged.connect(self.aspect_changed)
+        l.addRow(_('&Adjust Aspect Ratio:'), r)
         self.const_aspect = ca = QCheckBox(_('Keep the ratio of width to height fixed'))
         ca.toggled.connect(self.const_aspect_toggled)
         l.addRow(ca)
@@ -46,6 +58,16 @@ class Region(QDialog):
         self.resize(self.sizeHint())
         self.current_aspect = width / height
 
+    def aspect_changed(self):
+        inp = float(self.ratio_input.value())
+        if inp > 0 and inp != round(self.m_width/self.m_height, 2):
+            rw, rh = reduce_to_ratio(self.m_width, self.m_height, inp)
+            self.width_input.setValue(rw)
+            self.height_input.setValue(rh)
+        else:
+            self.width_input.setValue(self.m_width)
+            self.height_input.setValue(self.m_height)
+
     def const_aspect_toggled(self):
         if self.const_aspect.isChecked():
             self.current_aspect = self.width_input.value() / self.height_input.value()