diff --git a/Documentation/git-log.txt b/Documentation/git-log.txt
index 63c1dbe812e607..5a90f65b5e9d9c 100644
--- a/Documentation/git-log.txt
+++ b/Documentation/git-log.txt
@@ -64,6 +64,13 @@ include::pretty-options.txt[]
 --follow::
 	Continue listing the history of a file beyond renames.
 
+--log-size::
+	Before the log message print out its size in bytes. Intended
+	mainly for porcelain tools consumption. If git is unable to
+	produce a valid value size is set to zero.
+	Note that only message is considered, if also a diff is shown
+	its size is not included.
+
 <paths>...::
 	Show only commits that affect the specified paths.
 
diff --git a/log-tree.c b/log-tree.c
index 8624d5a39ca311..a6423718e76be3 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -295,6 +295,9 @@ void show_log(struct rev_info *opt, const char *sep)
 	if (opt->add_signoff)
 		len = append_signoff(&msgbuf, &msgbuf_len, len,
 				     opt->add_signoff);
+	if (opt->show_log_size)
+		printf("log size %i\n", len);
+
 	printf("%s%s%s", msgbuf, extra, sep);
 	free(msgbuf);
 }
diff --git a/revision.c b/revision.c
index 038693caba69a9..7d32a89b0eca85 100644
--- a/revision.c
+++ b/revision.c
@@ -1150,6 +1150,10 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, const ch
 					die("unknown date format %s", arg);
 				continue;
 			}
+			if (!strcmp(arg, "--log-size")) {
+				revs->show_log_size = 1;
+				continue;
+			}
 
 			/*
 			 * Grepping the commit log
diff --git a/revision.h b/revision.h
index f46b4d55a2c75e..98a0a8f3fa9db4 100644
--- a/revision.h
+++ b/revision.h
@@ -81,6 +81,7 @@ struct rev_info {
 	const char	*log_reencode;
 	const char	*subject_prefix;
 	int		no_inline;
+	int		show_log_size;
 
 	/* Filter by commit log message */
 	struct grep_opt	*grep_filter;