diff --git a/Userland/Libraries/LibWeb/CSS/Size.cpp b/Userland/Libraries/LibWeb/CSS/Size.cpp
index fc83076d23..2322c583fb 100644
--- a/Userland/Libraries/LibWeb/CSS/Size.cpp
+++ b/Userland/Libraries/LibWeb/CSS/Size.cpp
@@ -74,4 +74,24 @@ bool Size::contains_percentage() const
     }
 }
 
+String Size::to_string() const
+{
+    switch (m_type) {
+    case Type::Auto:
+        return "auto";
+    case Type::Length:
+    case Type::Percentage:
+        return m_length_percentage.to_string();
+    case Type::MinContent:
+        return "min-content";
+    case Type::MaxContent:
+        return "max-content";
+    case Type::FitContent:
+        return String::formatted("fit-content({})", m_length_percentage.to_string());
+    case Type::None:
+        return "none";
+    }
+    VERIFY_NOT_REACHED();
+}
+
 }
diff --git a/Userland/Libraries/LibWeb/CSS/Size.h b/Userland/Libraries/LibWeb/CSS/Size.h
index 31852807fb..6c86f9325d 100644
--- a/Userland/Libraries/LibWeb/CSS/Size.h
+++ b/Userland/Libraries/LibWeb/CSS/Size.h
@@ -63,6 +63,8 @@ public:
         return m_length_percentage.length();
     }
 
+    String to_string() const;
+
 private:
     Size(Type type, LengthPercentage);
 
@@ -71,3 +73,11 @@ private:
 };
 
 }
+
+template<>
+struct AK::Formatter<Web::CSS::Size> : Formatter<StringView> {
+    ErrorOr<void> format(FormatBuilder& builder, Web::CSS::Size const& size)
+    {
+        return Formatter<StringView>::format(builder, size.to_string());
+    }
+};