diff --git a/src/calibre/ebooks/mobi/mobiml.py b/src/calibre/ebooks/mobi/mobiml.py
index 432f78d027..53eefbc61f 100644
--- a/src/calibre/ebooks/mobi/mobiml.py
+++ b/src/calibre/ebooks/mobi/mobiml.py
@@ -51,6 +51,16 @@ def asfloat(value):
     return float(value)
 
 
+def convert_margin(style, which):
+    # percentage values come out too large when the user uses a non kindle
+    # output profile like the tablet profile
+    ans = asfloat(style[which])
+    raw = style._get(which)
+    if isinstance(raw, str) and '%' in raw:
+        ans = min(style._unit_convert(raw, base=600), ans)
+    return ans
+
+
 def isspace(text):
     if not text:
         return True
@@ -372,12 +382,12 @@ class MobiMLizer(object):
             if style['margin-left'] == 'auto' \
                and style['margin-right'] == 'auto':
                 istate.halign = 'center'
-            margin = asfloat(style['margin-left'])
+            margin = convert_margin(style, 'margin-left')
             padding = asfloat(style['padding-left'])
             if tag != 'body':
                 left = margin + padding
             istate.left += left
-            vmargin = asfloat(style['margin-top'])
+            vmargin = convert_margin(style, 'margin-top')
             bstate.vmargin = max((bstate.vmargin, vmargin))
             vpadding = asfloat(style['padding-top'])
             if vpadding > 0:
@@ -385,13 +395,13 @@ class MobiMLizer(object):
                 bstate.vmargin = 0
                 bstate.vpadding += vpadding
         elif not istate.href:
-            margin = asfloat(style['margin-left'])
+            margin = convert_margin(style, 'margin-left')
             padding = asfloat(style['padding-left'])
             lspace = margin + padding
             if lspace > 0:
                 spaces = int(round((lspace * 3) / style['font-size']))
                 elem.text = ('\xa0' * spaces) + (elem.text or '')
-            margin = asfloat(style['margin-right'])
+            margin = convert_margin(style, 'margin-right')
             padding = asfloat(style['padding-right'])
             rspace = margin + padding
             if rspace > 0:
@@ -610,7 +620,7 @@ class MobiMLizer(object):
                     para.getparent().remove(para)
             bstate.para = None
             bstate.istate = None
-            vmargin = asfloat(style['margin-bottom'])
+            vmargin = convert_margin(style, 'margin-bottom')
             bstate.vmargin = max((bstate.vmargin, vmargin))
             vpadding = asfloat(style['padding-bottom'])
             if vpadding > 0: