diff --git a/trans.sh b/trans.sh
index 8437371..3f7e8c6 100644
--- a/trans.sh
+++ b/trans.sh
@@ -507,8 +507,8 @@ create_part() {
             error_and_exit "Can't access Windows iso."
         fi
 
-        # 按1.1倍iso容量计算分区大小
-        part_size=$(grep 'Content-Length:' /tmp/headers.log | awk '{print int($2*1.1/1024/1024)}')
+        # 按iso容量计算分区大小，512m用于驱动和文件系统自身占用
+        part_size=$(grep 'Content-Length:' /tmp/headers.log | awk '{print int($2/1024/1024+512)}')
         if [ -z "$part_size" ]; then
             # 默认值，最大的iso 23h2 需要7g
             part_size=$((7 * 1024))