first command creates file with size of 10MB and not 1MB
:~/prashant/test$ dd if=/dev/zero of=file_name.txt bs=1024k count=10
10+0 records in
10+0 records out
10485760 bytes (10 MB, 10 MiB) copied, 0.00991439 s, 1.1 GB/s
:~/prashant/test$ du -h file_name.txt
10M file_name.txt
:~/prashant/test$