diff --git a/crates/oxc_formatter/src/formatter/mod.rs b/crates/oxc_formatter/src/formatter/mod.rs
index 76b984ddb6d96..fbc0de93a5f7f 100644
--- a/crates/oxc_formatter/src/formatter/mod.rs
+++ b/crates/oxc_formatter/src/formatter/mod.rs
@@ -354,8 +354,14 @@ pub fn format<'ast>(
     context: FormatContext<'ast>,
     arguments: Arguments<'_, 'ast>,
 ) -> FormatResult<Formatted<'ast>> {
+    // Pre-allocate buffer at 40% of source length (source_len * 2 / 5).
+    // Analysis of 4,891 VSCode files shows FormatElement buffer length is typically 19% of source (median),
+    // with 95th percentile at 30-38% across all file sizes. This 0.4x multiplier avoids
+    // reallocation for 95%+ of files.
+    let capacity = (context.source_text().len() * 2) / 5;
+
     let mut state = FormatState::new(context);
-    let mut buffer = VecBuffer::with_capacity(arguments.items().len(), &mut state);
+    let mut buffer = VecBuffer::with_capacity(capacity, &mut state);
 
     buffer.write_fmt(arguments)?;