diff --git a/src/wormhole/servers/transit_server.py b/src/wormhole/servers/transit_server.py
index da54e69..2412c89 100644
--- a/src/wormhole/servers/transit_server.py
+++ b/src/wormhole/servers/transit_server.py
@@ -10,6 +10,18 @@ HOUR = 60*MINUTE
 DAY = 24*HOUR
 MB = 1000*1000
 
+def round_to(size, coarseness):
+    return int(coarseness*(1+int((size-1)/coarseness)))
+
+def blur_size(size):
+    if size == 0:
+        return 0
+    if size < 1e6:
+        return round_to(size, 10e3)
+    if size < 1e9:
+        return round_to(size, 1e6)
+    return round_to(size, 100e6)
+
 class TransitConnection(protocol.Protocol):
     def __init__(self):
         self._got_token = False
@@ -173,6 +185,7 @@ class Transit(protocol.ServerFactory, service.MultiService):
         log.msg("Transit.recordUsage (%dB)" % total_bytes)
         if self._blur_usage:
             started = self._blur_usage * (started // self._blur_usage)
+            total_bytes = blur_size(total_bytes)
         self._db.execute("INSERT INTO `usage`"
                          " (`type`, `started`, `result`, `total_bytes`,"
                          "  `total_time`, `waiting_time`)"
diff --git a/src/wormhole/test/test_server.py b/src/wormhole/test/test_server.py
index 3b8be7e..978fa0d 100644
--- a/src/wormhole/test/test_server.py
+++ b/src/wormhole/test/test_server.py
@@ -8,7 +8,7 @@ from twisted.internet.threads import deferToThread
 from twisted.web.client import getPage, Agent, readBody
 from .. import __version__
 from .common import ServerBase
-from ..servers import relay_server
+from ..servers import relay_server, transit_server
 from ..twisted.eventsource_twisted import EventSource
 
 class Reachable(ServerBase, unittest.TestCase):
@@ -429,3 +429,23 @@ class Summary(unittest.TestCase):
                              (1, "quiet", 40, 9))
         self.failUnlessEqual(c._summarize(make_moods(None, "scary"), 41),
                              (1, "scary", 40, 9))
+
+class Transit(unittest.TestCase):
+    def test_blur_size(self):
+        blur = transit_server.blur_size
+        self.failUnlessEqual(blur(0), 0)
+        self.failUnlessEqual(blur(1), 10e3)
+        self.failUnlessEqual(blur(10e3), 10e3)
+        self.failUnlessEqual(blur(10e3+1), 20e3)
+        self.failUnlessEqual(blur(15e3), 20e3)
+        self.failUnlessEqual(blur(20e3), 20e3)
+        self.failUnlessEqual(blur(1e6), 1e6)
+        self.failUnlessEqual(blur(1e6+1), 2e6)
+        self.failUnlessEqual(blur(1.5e6), 2e6)
+        self.failUnlessEqual(blur(2e6), 2e6)
+        self.failUnlessEqual(blur(900e6), 900e6)
+        self.failUnlessEqual(blur(1000e6), 1000e6)
+        self.failUnlessEqual(blur(1050e6), 1100e6)
+        self.failUnlessEqual(blur(1100e6), 1100e6)
+        self.failUnlessEqual(blur(1150e6), 1200e6)
+