biomejs · ematipico · Nov 20, 2025 · Nov 19, 2025 · Nov 19, 2025 · Nov 19, 2025
diff --git a/.changeset/wise-dots-rush.md b/.changeset/wise-dots-rush.md
@@ -0,0 +1,25 @@
+---
+"@biomejs/biome": patch
+---
+
+Fixed CSS formatting of dimension units to use correct casing for `Q`, `Hz` and `kHz`.
+
+**Before:**
+
+``` css
+.cssUnits {
+  a: 1q;
+  b: 1hz;
+  c: 1khz;
+}
+```
+
+**After:**
+
+``` css
+.cssUnits {
+  a: 1Q;
+  b: 1Hz;
+  c: 1kHz;
+}
+```
diff --git a/crates/biome_css_formatter/src/css/value/regular_dimension.rs b/crates/biome_css_formatter/src/css/value/regular_dimension.rs
@@ -1,4 +1,4 @@
-use crate::{prelude::*, utils::string_utils::FormatTokenAsLowercase};
+use crate::{prelude::*, utils::string_utils::FormatDimensionUnit};
 use biome_css_syntax::{CssRegularDimension, CssRegularDimensionFields};
 use biome_formatter::{token::number::NumberFormatOptions, write};
 
@@ -15,7 +15,7 @@ impl FormatNodeRule<CssRegularDimension> for FormatCssRegularDimension {
             f,
             [
                 format_number_token(&value_token?, NumberFormatOptions::default()),
-                FormatTokenAsLowercase::from(unit_token?),
+                FormatDimensionUnit::from(unit_token?),
             ]
         )
     }

diff --git a/crates/biome_css_formatter/src/css/value/unknown_dimension.rs b/crates/biome_css_formatter/src/css/value/unknown_dimension.rs
@@ -1,4 +1,7 @@
-use crate::{prelude::*, utils::string_utils::FormatTokenAsLowercase};
+use crate::{
+    prelude::*,
+    utils::string_utils::{FormatDimensionUnit, FormatTokenAsLowercase},
+};
 use biome_css_syntax::{CssUnknownDimension, CssUnknownDimensionFields};
 use biome_formatter::write;
 
@@ -15,7 +18,7 @@ impl FormatNodeRule<CssUnknownDimension> for FormatCssUnknownDimension {
             f,
             [
                 FormatTokenAsLowercase::from(value_token?),
-                FormatTokenAsLowercase::from(unit_token?),
+                FormatDimensionUnit::from(unit_token?),
             ]
         );
         var_name

diff --git a/crates/biome_css_formatter/src/utils/string_utils.rs b/crates/biome_css_formatter/src/utils/string_utils.rs
@@ -296,3 +296,61 @@ impl<'token> LiteralStringNormaliser<'token> {
         }
     }
 }
+
+pub(crate) struct FormatDimensionUnit {
+    token: SyntaxToken<CssLanguage>,
+}
+
+impl From<SyntaxToken<CssLanguage>> for FormatDimensionUnit {
+    fn from(value: SyntaxToken<CssLanguage>) -> Self {
+        Self { token: value }
+    }
+}
+
+impl Format<CssFormatContext> for FormatDimensionUnit {
+    fn fmt(&self, f: &mut CssFormatter) -> FormatResult<()> {
+        let original = self.token.text_trimmed();
+
+        match original.to_ascii_lowercase_cow() {
+            Cow::Borrowed(lowercase) => {
+                if let Some(uppercase) = map_dimension_unit(lowercase) {
+                    write!(
+                        f,
+                        [format_replaced(
+                            &self.token,
+                            &text(&uppercase, self.token.text_trimmed_range().start()),
+                        )]
+                    )
+                } else {
+                    write!(f, [self.token.format()])
+                }
+            }
+
+            Cow::Owned(lowercase) => {
+                write!(
+                    f,
+                    [format_replaced(
+                        &self.token,
+                        &text(
+                            &map_dimension_unit(lowercase.as_str()).unwrap_or(lowercase),
+                            self.token.text_trimmed_range().start()
+                        ),
+                    )]
+                )
+            }
+        }
+    }
+}
+
+/// Most CSS dimension units can be formatted as lower case, but there are
+/// a few that are more commonly formatted with some uppercase characters.
+/// This maps those few cases to the correct casing. This matches the
+/// behavior of the Prettier formatter.
+fn map_dimension_unit(unit: &str) -> Option<String> {
+    match unit {
+        "hz" => Some(String::from("Hz")),
+        "khz" => Some(String::from("kHz")),
+        "q" => Some(String::from("Q")),
+        _ => None,
+    }
+}
diff --git a/crates/biome_css_formatter/tests/specs/css/units.css b/crates/biome_css_formatter/tests/specs/css/units.css
@@ -20,6 +20,7 @@
   a: 5CM;
   a: 5MM;
   a: 5Q;
+  a: 5q;
   a: 5IN;
   a: 5PT;
   a: 5PC;
@@ -30,7 +31,9 @@
   a: 5S;
   a: 5MS;
   a: 5HZ;
+  a: 5hz;
   a: 5KHZ;
+  a: 5kHz;
   a: 5DPI;
   a: 5DPCM;
   a: 5DPPX;
@@ -41,4 +44,4 @@
   a: 5Unknown;
   /* http://browserbu.gs/css-hacks/media-min-width-0-backslash-0/ */
   a: 0\0;
-}
+}
diff --git a/crates/biome_css_formatter/tests/specs/css/units.css.snap b/crates/biome_css_formatter/tests/specs/css/units.css.snap
@@ -2,7 +2,6 @@
 source: crates/biome_formatter_test/src/snapshot_builder.rs
 info: css/units.css
 ---
-
 # Input
 
 ```css
@@ -28,6 +27,7 @@ info: css/units.css
   a: 5CM;
   a: 5MM;
   a: 5Q;
+  a: 5q;
   a: 5IN;
   a: 5PT;
   a: 5PC;
@@ -38,7 +38,9 @@ info: css/units.css
   a: 5S;
   a: 5MS;
   a: 5HZ;
+  a: 5hz;
   a: 5KHZ;
+  a: 5kHz;
   a: 5DPI;
   a: 5DPCM;
   a: 5DPPX;
@@ -50,6 +52,7 @@ info: css/units.css
   /* http://browserbu.gs/css-hacks/media-min-width-0-backslash-0/ */
   a: 0\0;
 }
+
 ```
 
 
@@ -89,7 +92,8 @@ Quote style: Double Quotes
 	a: 5vmax;
 	a: 5cm;
 	a: 5mm;
-	a: 5q;
+	a: 5Q;
+	a: 5Q;
 	a: 5in;
 	a: 5pt;
 	a: 5pc;
@@ -99,8 +103,10 @@ Quote style: Double Quotes
 	a: 5rad;
 	a: 5s;
 	a: 5ms;
-	a: 5hz;
-	a: 5khz;
+	a: 5Hz;
+	a: 5Hz;
+	a: 5kHz;
+	a: 5kHz;
 	a: 5dpi;
 	a: 5dpcm;
 	a: 5dppx;
@@ -113,5 +119,3 @@ Quote style: Double Quotes
 	a: 0\0;
 }
 ```
-
-