diff --git a/src/modules/stock-count.ts b/src/modules/stock-count.ts
index ab86ed8..8207b89 100644
--- a/src/modules/stock-count.ts
+++ b/src/modules/stock-count.ts
@@ -33,3 +33,10 @@ export interface StockCountReportRow {
  * @returns 逐物料的差異報表列
  */
 export const buildReport = (diffs: StockCountDiff[]): StockCountReportRow[] => diffs.map((diff) => ({ materialId: diff.materialId, diff: diffQty(diff) }));
+
+/**
+ * 將差異報表列轉為 CSV 字串（依賴 F1 的報表列型別）
+ * @param rows - 差異報表列
+ * @returns 以換行分隔的 CSV 內容
+ */
+export const toCsv = (rows: StockCountReportRow[]): string => rows.map((row) => `${row.materialId},${row.diff}`).join("\n");