Compute the exact MB to type into Windows Disk Management so the result shows as a clean integer GB.
Enter the target size in GB and click Calculate. Three formulas are compared: (1) Classic one-head — (N−1)×1024+1023, the long-standing trick that lands on a clean integer GB on legacy MBR / 512-byte-sector disks (e.g. 10 GB → 10239 MB). (2) Modern aligned — N×1024−1, suits newer GPT + 4K-native (4Kn) disks with 1 MB partition alignment. (3) Naive — N×1024, the mathematically exact MB; Windows usually shows N−1 GB due to NTFS overhead. Pick the value matching your disk layout and copy it.