diff --git a/Documentation/git-for-each-ref.txt b/Documentation/git-for-each-ref.txt
index 2db9779d54..833641eacd 100644
--- a/Documentation/git-for-each-ref.txt
+++ b/Documentation/git-for-each-ref.txt
@@ -235,6 +235,9 @@ and `date` to extract the named component.
 The complete message of a commit or tag object is `contents`. This
 field can also be used in the following ways:
 
+contents:size::
+	The size in bytes of the complete message.
+
 contents:subject::
 	The "subject" of the commit or tag message.  It's actually the
 	concatenation of all lines of the commit message up to the
diff --git a/ref-filter.c b/ref-filter.c
index bf7b70299b..036a95d0d2 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -127,7 +127,8 @@ static struct used_atom {
 			unsigned int nobracket : 1, push : 1, push_remote : 1;
 		} remote_ref;
 		struct {
-			enum { C_BARE, C_BODY, C_BODY_DEP, C_LINES, C_SIG, C_SUB, C_TRAILERS } option;
+			enum { C_BARE, C_BODY, C_BODY_DEP, C_LENGTH,
+			       C_LINES, C_SIG, C_SUB, C_TRAILERS } option;
 			struct process_trailer_options trailer_opts;
 			unsigned int nlines;
 		} contents;
@@ -338,6 +339,8 @@ static int contents_atom_parser(const struct ref_format *format, struct used_ato
 		atom->u.contents.option = C_BARE;
 	else if (!strcmp(arg, "body"))
 		atom->u.contents.option = C_BODY;
+	else if (!strcmp(arg, "size"))
+		atom->u.contents.option = C_LENGTH;
 	else if (!strcmp(arg, "signature"))
 		atom->u.contents.option = C_SIG;
 	else if (!strcmp(arg, "subject"))
@@ -1253,6 +1256,8 @@ static void grab_sub_body_contents(struct atom_value *val, int deref, void *buf)
 			v->s = copy_subject(subpos, sublen);
 		else if (atom->u.contents.option == C_BODY_DEP)
 			v->s = xmemdupz(bodypos, bodylen);
+		else if (atom->u.contents.option == C_LENGTH)
+			v->s = xstrfmt("%ld", strlen(subpos));
 		else if (atom->u.contents.option == C_BODY)
 			v->s = xmemdupz(bodypos, nonsiglen);
 		else if (atom->u.contents.option == C_SIG)
diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
index da59fadc5d..ceee8d9372 100755
--- a/t/t6300-for-each-ref.sh
+++ b/t/t6300-for-each-ref.sh
@@ -125,6 +125,7 @@ test_atom head contents:body ''
 test_atom head contents:signature ''
 test_atom head contents 'Initial
 '
+test_atom head contents:size '8'
 test_atom head HEAD '*'
 
 test_atom tag refname refs/tags/testtag
@@ -170,6 +171,7 @@ test_atom tag contents:body ''
 test_atom tag contents:signature ''
 test_atom tag contents 'Tagging at 1151968727
 '
+test_atom tag contents:size '22'
 test_atom tag HEAD ' '
 
 test_expect_success 'Check invalid atoms names are errors' '
@@ -580,6 +582,7 @@ test_atom refs/tags/subject-body contents 'the subject line
 first body line
 second body line
 '
+test_atom refs/tags/subject-body contents:size '51'
 
 test_expect_success 'create tag with multiline subject' '
 	cat >msg <<-\EOF &&
@@ -606,6 +609,7 @@ second subject line
 first body line
 second body line
 '
+test_atom refs/tags/multiline contents:size '73'
 
 test_expect_success GPG 'create signed tags' '
 	git tag -s -m "" signed-empty &&
@@ -622,6 +626,16 @@ sig='-----BEGIN PGP SIGNATURE-----
 -----END PGP SIGNATURE-----
 '
 
+# We cannot use test_atom to check contents:size of signed tags due to sanitize_pgp
+test_tag_contents_size_pgp () {
+	ref="$1"
+	test_expect_success $PREREQ "basic atom: $ref contents:size" "
+		git cat-file tag $ref | tail -n +6 | wc -c >expected &&
+		git for-each-ref --format='%(contents:size)' $ref >actual &&
+		test_cmp expected actual
+	"
+}
+
 PREREQ=GPG
 test_atom refs/tags/signed-empty subject ''
 test_atom refs/tags/signed-empty contents:subject ''
@@ -629,6 +643,7 @@ test_atom refs/tags/signed-empty body "$sig"
 test_atom refs/tags/signed-empty contents:body ''
 test_atom refs/tags/signed-empty contents:signature "$sig"
 test_atom refs/tags/signed-empty contents "$sig"
+test_tag_contents_size_pgp refs/tags/signed-empty
 
 test_atom refs/tags/signed-short subject 'subject line'
 test_atom refs/tags/signed-short contents:subject 'subject line'
@@ -637,6 +652,7 @@ test_atom refs/tags/signed-short contents:body ''
 test_atom refs/tags/signed-short contents:signature "$sig"
 test_atom refs/tags/signed-short contents "subject line
 $sig"
+test_tag_contents_size_pgp refs/tags/signed-short
 
 test_atom refs/tags/signed-long subject 'subject line'
 test_atom refs/tags/signed-long contents:subject 'subject line'
@@ -649,6 +665,7 @@ test_atom refs/tags/signed-long contents "subject line
 
 body contents
 $sig"
+test_tag_contents_size_pgp refs/tags/signed-long
 
 test_expect_success 'set up multiple-sort tags' '
 	for when in 100000 200000
