diff --git a/Libraries/LibWeb/CSS/ResolvedCSSStyleDeclaration.cpp b/Libraries/LibWeb/CSS/ResolvedCSSStyleDeclaration.cpp
index 244bfe251af..702155cd3f8 100644
--- a/Libraries/LibWeb/CSS/ResolvedCSSStyleDeclaration.cpp
+++ b/Libraries/LibWeb/CSS/ResolvedCSSStyleDeclaration.cpp
@@ -243,7 +243,7 @@ RefPtr<CSSStyleValue const> ResolvedCSSStyleDeclaration::style_value_for_propert
 
         // -> block-size
         // -> height
-        // FIXME: -> inline-size
+        // -> inline-size
         // -> margin-block-end
         // -> margin-block-start
         // -> margin-bottom
@@ -277,6 +277,13 @@ RefPtr<CSSStyleValue const> ResolvedCSSStyleDeclaration::style_value_for_propert
             return style_value_for_size(Size::make_px(maybe_used_height.release_value()));
         return style_value_for_size(layout_node.computed_values().height());
     }
+    case PropertyID::InlineSize: {
+        auto writing_mode = layout_node.computed_values().writing_mode();
+        auto is_vertically_oriented = first_is_one_of(writing_mode, WritingMode::VerticalLr, WritingMode::VerticalRl);
+        if (is_vertically_oriented)
+            return style_value_for_property(layout_node, PropertyID::Height);
+        return style_value_for_property(layout_node, PropertyID::Width);
+    }
     case PropertyID::MarginBlockEnd:
         if (auto maybe_used_value = used_value_for_property([&](auto const& paintable_box) { return pixels_for_pixel_box_logical_side(layout_node, paintable_box.box_model().margin, LogicalSide::BlockEnd); }); maybe_used_value.has_value())
             return LengthStyleValue::create(Length::make_px(maybe_used_value.release_value()));
diff --git a/Tests/LibWeb/Text/expected/css/CSSStyleDeclaration-all-supported-properties-and-default-values.txt b/Tests/LibWeb/Text/expected/css/CSSStyleDeclaration-all-supported-properties-and-default-values.txt
index 8b3ec729747..40e439a2d30 100644
--- a/Tests/LibWeb/Text/expected/css/CSSStyleDeclaration-all-supported-properties-and-default-values.txt
+++ b/Tests/LibWeb/Text/expected/css/CSSStyleDeclaration-all-supported-properties-and-default-values.txt
@@ -374,8 +374,8 @@ All supported properties and their default values exposed from CSSStyleDeclarati
 'height': '0px'
 'imageRendering': 'auto'
 'image-rendering': 'auto'
-'inlineSize': 'auto'
-'inline-size': 'auto'
+'inlineSize': '284px'
+'inline-size': '284px'
 'inset': 'auto auto auto auto'
 'insetBlock': 'auto auto auto auto'
 'inset-block': 'auto auto auto auto'
diff --git a/Tests/LibWeb/Text/expected/css/getComputedStyle-print-all.txt b/Tests/LibWeb/Text/expected/css/getComputedStyle-print-all.txt
index 6eca7cfd63f..6e3bca9d6f2 100644
--- a/Tests/LibWeb/Text/expected/css/getComputedStyle-print-all.txt
+++ b/Tests/LibWeb/Text/expected/css/getComputedStyle-print-all.txt
@@ -137,7 +137,7 @@ grid-template-areas: none
 grid-template-columns: auto
 grid-template-rows: auto
 height: 1932px
-inline-size: auto
+inline-size: 784px
 inset-block-end: auto
 inset-block-start: auto
 inset-inline-end: auto
diff --git a/Tests/LibWeb/Text/expected/wpt-import/css/css-logical/parsing/inline-size-computed.txt b/Tests/LibWeb/Text/expected/wpt-import/css/css-logical/parsing/inline-size-computed.txt
new file mode 100644
index 00000000000..f4997caa8da
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/css/css-logical/parsing/inline-size-computed.txt
@@ -0,0 +1,12 @@
+Harness status: OK
+
+Found 7 tests
+
+7 Pass
+Pass	Property inline-size value 'auto'
+Pass	Property inline-size value '10px'
+Pass	Property inline-size value '20%'
+Pass	Property inline-size value 'calc(0.5em + 10px)'
+Pass	Property inline-size value 'calc(-0.5em + 10px)'
+Pass	Property inline-size value 'min-content'
+Pass	Property inline-size value 'max-content'
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/input/wpt-import/css/css-logical/parsing/inline-size-computed.html b/Tests/LibWeb/Text/input/wpt-import/css/css-logical/parsing/inline-size-computed.html
new file mode 100644
index 00000000000..dea34f4d3c8
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/css/css-logical/parsing/inline-size-computed.html
@@ -0,0 +1,44 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<title>CSS Logical Properties and Values: getComputedStyle().inlineSize</title>
+<link rel="help" href="https://drafts.csswg.org/css-logical-1/#dimension-properties">
+<meta name="assert" content="inline-size computed value is an absolute length.">
+<script src="../../../resources/testharness.js"></script>
+<script src="../../../resources/testharnessreport.js"></script>
+<script src="../../../css/support/computed-testcommon.js"></script>
+<style>
+  #parent {
+    width: 200px;
+  }
+  #target {
+    width: 0px;
+    height: 0px;
+    font-size: 40px;
+  }
+  #child {
+    width: 60px;
+  }
+</style>
+</head>
+<body>
+<div id="parent">
+  <div id="target">
+    <div id="child">
+    </div>
+  </div>
+</div>
+<script>
+test_computed_value("inline-size", "auto", "200px"); // parent width
+
+test_computed_value("inline-size", "10px");
+test_computed_value("inline-size", "20%", "40px");
+test_computed_value("inline-size", "calc(0.5em + 10px)", "30px");
+test_computed_value("inline-size", "calc(-0.5em + 10px)", "0px");
+
+test_computed_value("inline-size", "min-content", "60px"); // child width
+test_computed_value("inline-size", "max-content", "60px");
+</script>
+</body>
+</html>