diff --git a/chrome/test/data/pdf/viewer_properties_dialog_test.js b/chrome/test/data/pdf/viewer_properties_dialog_test.js
index cc937c5ffca0f..ab668fb7bd349 100644
--- a/chrome/test/data/pdf/viewer_properties_dialog_test.js
+++ b/chrome/test/data/pdf/viewer_properties_dialog_test.js
@@ -59,7 +59,7 @@ const tests = [
      ['pdf-producer', 'fixup_pdf_template.py'],
      ['pdf-version', '1.7'],
      ['page-count', '1'],
-     ['page-size', '2.78 × 2.78 in (portrait)'],
+     ['page-size', '2.78 × 2.78 in (square)'],
      ['fast-web-view', 'No'],
     ].forEach(([field, expectedValue]) => assertField(field, expectedValue));
 
diff --git a/components/pdf_strings.grdp b/components/pdf_strings.grdp
index 0f1ef6784a448..7181ca1513c2e 100644
--- a/components/pdf_strings.grdp
+++ b/components/pdf_strings.grdp
@@ -97,6 +97,9 @@
     <message name="IDS_PDF_PROPERTIES_PAGE_SIZE_LANDSCAPE" desc="Label for a landscape page orientation.">
       landscape
     </message>
+    <message name="IDS_PDF_PROPERTIES_PAGE_SIZE_SQUARE" desc="Label for a square page that has neither portrait nor landscape orientation.">
+      square
+    </message>
     <message name="IDS_PDF_PROPERTIES_PAGE_SIZE_VARIABLE" desc="Value for the page size of a PDF that lacks a uniform page size.">
       Varies
     </message>
diff --git a/components/pdf_strings_grdp/IDS_PDF_PROPERTIES_PAGE_SIZE_SQUARE.png.sha1 b/components/pdf_strings_grdp/IDS_PDF_PROPERTIES_PAGE_SIZE_SQUARE.png.sha1
new file mode 100644
index 0000000000000..f33a81a49cbb7
--- /dev/null
+++ b/components/pdf_strings_grdp/IDS_PDF_PROPERTIES_PAGE_SIZE_SQUARE.png.sha1
@@ -0,0 +1 @@
+161d76850b84697ce3498aec6b98e927b4fefc86
\ No newline at end of file
diff --git a/pdf/ui/document_properties.cc b/pdf/ui/document_properties.cc
index 2727c6b6ebb99..d6c9e9078d284 100644
--- a/pdf/ui/document_properties.cc
+++ b/pdf/ui/document_properties.cc
@@ -53,11 +53,15 @@ std::u16string FormatLengthInMillimeters(int length_points) {
 
 // Returns the localized string for the orientation.
 std::u16string GetOrientation(const gfx::Size& size) {
-  // TODO(crbug.com/1184345): Add a string for square sizes such that they are
-  // not displayed as "portrait".
-  return l10n_util::GetStringUTF16(
-      size.height() >= size.width() ? IDS_PDF_PROPERTIES_PAGE_SIZE_PORTRAIT
-                                    : IDS_PDF_PROPERTIES_PAGE_SIZE_LANDSCAPE);
+  int message_id;
+  if (size.height() > size.width())
+    message_id = IDS_PDF_PROPERTIES_PAGE_SIZE_PORTRAIT;
+  else if (size.height() < size.width())
+    message_id = IDS_PDF_PROPERTIES_PAGE_SIZE_LANDSCAPE;
+  else
+    message_id = IDS_PDF_PROPERTIES_PAGE_SIZE_SQUARE;
+
+  return l10n_util::GetStringUTF16(message_id);
 }
 
 bool ShowInches() {
diff --git a/pdf/ui/document_properties_unittest.cc b/pdf/ui/document_properties_unittest.cc
index 18c2fae9c8be4..21a62a6b21102 100644
--- a/pdf/ui/document_properties_unittest.cc
+++ b/pdf/ui/document_properties_unittest.cc
@@ -53,7 +53,7 @@ class FormatPageSizeMillimetersTest : public FormatPageSizeTest {
 };
 
 TEST_F(FormatPageSizeMillimetersTest, EmptySize) {
-  EXPECT_EQ(FormatPageSize(gfx::Size()), u"0 × 0 mm (portrait)");
+  EXPECT_EQ(FormatPageSize(gfx::Size()), u"0 × 0 mm (square)");
 }
 
 TEST_F(FormatPageSizeMillimetersTest, Portrait) {
@@ -65,12 +65,12 @@ TEST_F(FormatPageSizeMillimetersTest, Landscape) {
 }
 
 TEST_F(FormatPageSizeMillimetersTest, Square) {
-  EXPECT_EQ(FormatPageSize(gfx::Size(100, 100)), u"35 × 35 mm (portrait)");
+  EXPECT_EQ(FormatPageSize(gfx::Size(100, 100)), u"35 × 35 mm (square)");
 }
 
 TEST_F(FormatPageSizeMillimetersTest, Large) {
   EXPECT_EQ(FormatPageSize(gfx::Size(72000, 72000)),
-            u"25,400 × 25,400 mm (portrait)");
+            u"25,400 × 25,400 mm (square)");
 }
 
 class FormatPageSizeMillimetersPeriodSeparatorTest : public FormatPageSizeTest {
@@ -80,7 +80,7 @@ class FormatPageSizeMillimetersPeriodSeparatorTest : public FormatPageSizeTest {
 
 TEST_F(FormatPageSizeMillimetersPeriodSeparatorTest, Large) {
   EXPECT_EQ(FormatPageSize(gfx::Size(72000, 72000)),
-            u"25.400 × 25.400 mm (portrait)");
+            u"25.400 × 25.400 mm (square)");
 }
 
 class FormatPageSizeInchesTest : public FormatPageSizeTest {
@@ -89,7 +89,7 @@ class FormatPageSizeInchesTest : public FormatPageSizeTest {
 };
 
 TEST_F(FormatPageSizeInchesTest, EmptySize) {
-  EXPECT_EQ(FormatPageSize(gfx::Size()), u"0.00 × 0.00 in (portrait)");
+  EXPECT_EQ(FormatPageSize(gfx::Size()), u"0.00 × 0.00 in (square)");
 }
 
 TEST_F(FormatPageSizeInchesTest, Portrait) {
@@ -101,12 +101,12 @@ TEST_F(FormatPageSizeInchesTest, Landscape) {
 }
 
 TEST_F(FormatPageSizeInchesTest, Square) {
-  EXPECT_EQ(FormatPageSize(gfx::Size(100, 100)), u"1.39 × 1.39 in (portrait)");
+  EXPECT_EQ(FormatPageSize(gfx::Size(100, 100)), u"1.39 × 1.39 in (square)");
 }
 
 TEST_F(FormatPageSizeInchesTest, Large) {
   EXPECT_EQ(FormatPageSize(gfx::Size(72000, 72000)),
-            u"1,000.00 × 1,000.00 in (portrait)");
+            u"1,000.00 × 1,000.00 in (square)");
 }
 
 TEST(FormatPdfVersion, Valid) {