diff --git a/pydu/unit.py b/pydu/unit.py
new file mode 100644
index 0000000..851a523
--- /dev/null
+++ b/pydu/unit.py
@@ -0,0 +1,31 @@
+
+
+BYTE_UNITS = ('B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB')
+
+
+class Bytes(object):
+    """
+    Supply several methods dealing with bytes.
+    """
+    def __init__(self, bytes):
+        self.bytes = bytes
+
+    def convert(self, unit=None, multiple=1024):
+        """
+        Convert bytes in give unit.
+        If `unit` is None, convert bytes in suitable unit.
+        Convert `multiple` is default to be 1024.
+        """
+        step = 0
+        if not unit:
+            while self.bytes >= multiple and step < len(BYTE_UNITS) - 1:
+                self.bytes /= multiple
+                step += 1
+            unit = BYTE_UNITS[step]
+
+        else:  # convert to specific unit
+            index_of_unit = BYTE_UNITS.index(unit)
+            while len(BYTE_UNITS) - 1 > step and index_of_unit != step:
+                self.bytes /= multiple
+                step += 1
+        return self.bytes, unit
diff --git a/tests/test_unit.py b/tests/test_unit.py
new file mode 100644
index 0000000..ffc664f
--- /dev/null
+++ b/tests/test_unit.py
@@ -0,0 +1,8 @@
+from pydu.unit import Bytes
+
+
+class TestBytes:
+    def test_convert(self):
+        assert Bytes(1024*1024).convert() == (1, 'MB')
+        assert Bytes(1024*1024).convert(unit='KB') == (1024, 'KB')
+        assert Bytes(1000).convert(multiple=1000) == (1, 'KB')