diff --git a/library/src/main/java/com/liulishuo/filedownloader/download/DownloadLaunchRunnable.java b/library/src/main/java/com/liulishuo/filedownloader/download/DownloadLaunchRunnable.java
index 7f955995..e4d523bb 100644
--- a/library/src/main/java/com/liulishuo/filedownloader/download/DownloadLaunchRunnable.java
+++ b/library/src/main/java/com/liulishuo/filedownloader/download/DownloadLaunchRunnable.java
@@ -537,7 +537,7 @@ private void handleTrialConnectResult(Map<String, List<String>> requestHeader,
 
         redirectedUrl = connectTask.getFinalRedirectedUrl();
         if (acceptPartial || onlyFromBeginning) {
-            final long totalLength = FileDownloadUtils.findInstanceLengthForTrial(id, connection);
+            final long totalLength = FileDownloadUtils.findInstanceLengthForTrial(connection);
 
             // update model
             String fileName = null;
diff --git a/library/src/main/java/com/liulishuo/filedownloader/util/FileDownloadUtils.java b/library/src/main/java/com/liulishuo/filedownloader/util/FileDownloadUtils.java
index 97703478..09d8fa24 100644
--- a/library/src/main/java/com/liulishuo/filedownloader/util/FileDownloadUtils.java
+++ b/library/src/main/java/com/liulishuo/filedownloader/util/FileDownloadUtils.java
@@ -555,9 +555,9 @@ public static boolean isAcceptRange(int responseCode, FileDownloadConnection con
     // because of we using one of two HEAD method to request or using range:0-0 to trial connection
     // only if connection api not support, so we test content-range first and then test
     // content-length.
-    public static long findInstanceLengthForTrial(int id, FileDownloadConnection connection) {
+    public static long findInstanceLengthForTrial(FileDownloadConnection connection) {
         long length = findInstanceLengthFromContentRange(connection);
-        if (length < 0) length = findContentLength(id, connection);
+        if (length < 0) length = findInstanceLengthFromContentLength(connection);
         if (length < 0) length = TOTAL_VALUE_IN_CHUNKED_RESOURCE;
         // the response of HEAD method is not very canonical sometimes(it depends on server
         // implementation)
@@ -571,14 +571,24 @@ public static long findInstanceLengthForTrial(int id, FileDownloadConnection con
     }
 
     public static long findInstanceLengthFromContentRange(FileDownloadConnection connection) {
-        return parseContentRangeFoInstanceLength(
-                connection.getResponseHeaderField("Content-Range"));
+        return parseContentRangeFoInstanceLength(getContentRangeHeader(connection));
+    }
+
+    private static String getContentRangeHeader(FileDownloadConnection connection) {
+        return  connection.getResponseHeaderField("Content-Range");
+    }
+
+    public static long findInstanceLengthFromContentLength(FileDownloadConnection connection) {
+        return convertContentLengthString(connection.getResponseHeaderField("Content-Length"));
     }
 
     public static long findContentLength(final int id, FileDownloadConnection connection) {
-        long contentLength = FileDownloadUtils
-                .convertContentLengthString(connection.getResponseHeaderField("Content-Length"));
-        if (contentLength < 0) contentLength = findInstanceLengthFromContentRange(connection);
+        long contentLength = findInstanceLengthFromContentLength(connection);
+        if (contentLength < 0) {
+            final String contentRange = getContentRangeHeader(connection);
+            contentLength = parseContentLengthFromContentRange(contentRange);
+        }
+
         final String transferEncoding = connection.getResponseHeaderField("Transfer-Encoding");
 
         if (contentLength < 0) {
@@ -610,6 +620,24 @@ public static long findContentLength(final int id, FileDownloadConnection connec
         return contentLength;
     }
 
+    public static long parseContentLengthFromContentRange(String contentRange) {
+        if (contentRange == null || contentRange.length() == 0) return -1;
+        final String pattern = "bytes (\\d+)-(\\d+)/\\d+";
+        try {
+            final Pattern r = Pattern.compile(pattern);
+            final Matcher m = r.matcher(contentRange);
+            if (m.find()) {
+                final long rangeStart = Long.parseLong(m.group(1));
+                final long rangeEnd = Long.parseLong(m.group(2));
+                return rangeEnd - rangeStart + 1;
+            }
+        }catch (Exception e) {
+            FileDownloadLog.e(FileDownloadUtils.class, e, "parse content length" +
+                    " from content range error");
+        }
+        return -1;
+    }
+
     public static String findFilename(FileDownloadConnection connection, String url) {
         String filename = FileDownloadUtils.parseContentDisposition(connection.
                 getResponseHeaderField("Content-Disposition"));
diff --git a/library/src/test/java/com/liulishuo/filedownloader/util/FileDownloadUtilsTest.java b/library/src/test/java/com/liulishuo/filedownloader/util/FileDownloadUtilsTest.java
index 933493a9..8c06f59f 100644
--- a/library/src/test/java/com/liulishuo/filedownloader/util/FileDownloadUtilsTest.java
+++ b/library/src/test/java/com/liulishuo/filedownloader/util/FileDownloadUtilsTest.java
@@ -35,4 +35,28 @@ public void parseContentDisposition() {
         assertThat(filename).isEqualTo("genome.jpeg");
     }
 
+    @Test
+    public void parseContentLengthFromContentRange_withNullContentRange() {
+        long length = FileDownloadUtils.parseContentLengthFromContentRange(null);
+        assertThat(length).isEqualTo(-1);
+    }
+
+    @Test
+    public void parseContentLengthFromContentRange_withEmptyContentRange() {
+        long length = FileDownloadUtils.parseContentLengthFromContentRange("");
+        assertThat(length).isEqualTo(-1);
+    }
+
+    @Test
+    public void parseContentLengthFromContentRange_withStartToEndRange() {
+        long length = FileDownloadUtils.parseContentLengthFromContentRange("bytes 25086300-37629450/37629451");
+        assertThat(length).isEqualTo(12543151);
+    }
+
+    @Test
+    public void parseContentLengthFromContentRange_withUnavailableContentRange() {
+        long length = FileDownloadUtils.parseContentLengthFromContentRange("bytes 0-/37629451");
+        assertThat(length).isEqualTo(-1);
+    }
+
 }
\ No newline at end of file