diff --git a/src/main/java/com/interplug/qcast/biz/estimate/EstimateService.java b/src/main/java/com/interplug/qcast/biz/estimate/EstimateService.java
index d5e03100..253d7556 100644
--- a/src/main/java/com/interplug/qcast/biz/estimate/EstimateService.java
+++ b/src/main/java/com/interplug/qcast/biz/estimate/EstimateService.java
@@ -1447,7 +1447,12 @@ public class EstimateService {
       roofInfoResponse.setRoofVolList(roofVolList);
 
       // 인증용량 구하기 (지붕면마다 모듈과 각각의 PCS의 총 용량을 서로 비교해 낮은쪽 용량으로 합산)
-      roofInfoResponse.setCertVolKw(estimateMapper.selectEstimateRoofCertVolKw(estimateRequest));
+      // 2026-06-05: SQL 은 W 합만 반환. kW 변환·3자리 절사(FLOOR)는 모듈용량(totVolKw)과 동일하게 처리 — FLOAT 나눗셈 잔여 방지
+      String certVolW = estimateMapper.selectEstimateRoofCertVolKw(estimateRequest);
+      roofInfoResponse.setCertVolKw(String.valueOf(
+              new BigDecimal(StringUtils.isEmpty(certVolW) ? "0" : certVolW)
+                      .multiply(new BigDecimal("0.001"))
+                      .setScale(3, RoundingMode.FLOOR)));
 
       //방위값
       CanvasPopupStatus cps =  canvasPopupStatusService.selectCanvasPopupStatus(estimateResponse.getObjectNo(), Integer.parseInt(estimateResponse.getPlanNo()), "1");
diff --git a/src/main/resources/mappers/estimate/estimateMapper.xml b/src/main/resources/mappers/estimate/estimateMapper.xml
index d7f94d6e..e8d80aa4 100644
--- a/src/main/resources/mappers/estimate/estimateMapper.xml
+++ b/src/main/resources/mappers/estimate/estimateMapper.xml
@@ -467,9 +467,8 @@
                  GROUP BY CIRCUIT_NO, CIRCUIT_ITEM_ID, CIRCUIT_CFG, CIRCUIT_SUM, PNOW_W
                      )
 
-                -- 2026-05-22: FLOAT ROUND 결과의 IEEE754 잔여(예: 5.5600000000000005) 차단 위해 DECIMAL 캐스팅
-                -- 2026-06-02: モジュール容量(totVolKw, setScale(3,FLOOR))과 동일 표시 위해 3자리 절사 + DECIMAL(18,3) 마감 (ROUND 3번째 인자=1 → 절사)
-                SELECT CAST(ROUND((SUM(MIN_VALUE) / 1000), 3, 1) AS DECIMAL(18,3))  AS CERT_VOL_KW
+                -- 2026-06-05: SQL 은 W 합만 DECIMAL 로 정확히 반환. kW 변환·3자리 절사(FLOOR)는 모듈용량(totVolKw)과 동일하게 Java BigDecimal 에서 수행 → FLOAT 나눗셈 잔여(5.6899999999999995 / 5.339) 원천 차단
+                SELECT CAST(SUM(MIN_VALUE) AS DECIMAL(18,3))  AS CERT_VOL_W
                 FROM CIRCUIT_AGG
 
         ]]>