diff --git a/arrow-row/src/lib.rs b/arrow-row/src/lib.rs
index 72a295627ed2..aa6543485fe3 100644
--- a/arrow-row/src/lib.rs
+++ b/arrow-row/src/lib.rs
@@ -1131,8 +1131,8 @@ impl Rows {
     pub fn size(&self) -> usize {
         // Size of fields is accounted for as part of RowConverter
         std::mem::size_of::<Self>()
-            + self.buffer.len()
-            + self.offsets.len() * std::mem::size_of::<usize>()
+            + self.buffer.capacity()
+            + self.offsets.capacity() * std::mem::size_of::<usize>()
     }
 
     /// Create a [BinaryArray] from the [Rows] data without reallocating the
@@ -4050,4 +4050,47 @@ mod tests {
         // "a" < "z"
         assert!(rows.row(3) < rows.row(1));
     }
+
+    #[test]
+    fn rows_size_should_count_for_capacity() {
+        let row_converter = RowConverter::new(vec![SortField::new(DataType::UInt8)]).unwrap();
+
+        let empty_rows_size_with_preallocate_rows_and_data = {
+            let rows = row_converter.empty_rows(1000, 1000);
+
+            rows.size()
+        };
+        let empty_rows_size_with_preallocate_rows = {
+            let rows = row_converter.empty_rows(1000, 0);
+
+            rows.size()
+        };
+        let empty_rows_size_with_preallocate_data = {
+            let rows = row_converter.empty_rows(0, 1000);
+
+            rows.size()
+        };
+        let empty_rows_size_without_preallocate = {
+            let rows = row_converter.empty_rows(0, 0);
+
+            rows.size()
+        };
+
+        assert!(
+            empty_rows_size_with_preallocate_rows_and_data > empty_rows_size_with_preallocate_rows,
+            "{empty_rows_size_with_preallocate_rows_and_data} should be larger than {empty_rows_size_with_preallocate_rows}"
+        );
+        assert!(
+            empty_rows_size_with_preallocate_rows_and_data > empty_rows_size_with_preallocate_data,
+            "{empty_rows_size_with_preallocate_rows_and_data} should be larger than {empty_rows_size_with_preallocate_data}"
+        );
+        assert!(
+            empty_rows_size_with_preallocate_rows > empty_rows_size_without_preallocate,
+            "{empty_rows_size_with_preallocate_rows} should be larger than {empty_rows_size_without_preallocate}"
+        );
+        assert!(
+            empty_rows_size_with_preallocate_data > empty_rows_size_without_preallocate,
+            "{empty_rows_size_with_preallocate_data} should be larger than {empty_rows_size_without_preallocate}"
+        );
+    }
 }