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Enter your target partition size in GB to calculate the MB value needed for an exact whole-number display in Windows—no more 99.9 GB partitions.
Enter the partition size you want the system to display as a whole number, in GB.
NTFS is estimated using cylinder alignment; FAT32 uses a commonly used whole-number partition formula.
Enter a target size to view the recommended MB values for NTFS and FAT32.
Creating a 100 GB partition on a new drive? You enter 102400 in the New Simple Volume wizard, click Finish, and Windows shows 99.9 GB instead. You’re not alone—this is a long-standing quirk of Windows partitioning. Our Integer Disk Partition Calculator solves that last 0.1 GB problem. No trial and error or formulas to memorize: enter your target size in GB and get the exact MB value to use.
The Integer Disk Partition Calculator tells you how many MB to enter when creating a partition in Windows Disk Management or Windows Setup so it appears as a whole number of GB in File Explorer—for example, 100.0 GB instead of 99.9 GB. Simply tell it, “I want N GB,” and it tells you, “Enter X MB when creating the partition.” This is not a unit-conversion mistake. When an NTFS partition is formatted, a small amount of space is reserved for metadata, making the usable capacity slightly smaller than the allocated size and causing a decimal display. The calculator includes NTFS compensation, so you only need to choose the whole-number capacity you want.
Windows uses binary units: 1 GB = 1024 MB. However, entering 1024 times your desired GB value alone does not produce a whole-number display. NTFS uses part of the partition for metadata such as the Master File Table (MFT) and logs. This overhead is roughly four times the partition size in MB, minus an offset. Based on extensive testing, use this formula for an integer NTFS partition:
MB = (G - 1) × 4 + 1024 × G
Where:
G — the whole-number GB capacity you want to see in This PC, such as 100, 200, or 500;
MB — the value to enter in the New Simple Volume size field.
In practical terms, the formula starts with 1024 × G, then adds compensation for NTFS metadata at about 4 MB per GB while accounting for a 4 MB offset. This lets Windows display the finished partition as an exact whole-number GB value. This formula applies to NTFS only. FAT32 uses different compensation rules and usually needs more complex adjustments; this calculator returns NTFS results by default.
Open the calculator to find two main areas: the input on the left and the result on the right.
1. Enter the whole-number capacity you want, such as “100,” in the “Desired partition size (GB)” field.
2. Leave the file system set to “NTFS,” the format this calculator is designed for.
3. Click “Calculate.”
4. The “Size to enter (MB)” field will immediately show a value, such as “102796.”
5. Open Windows Disk Management, enter that MB value, then create and format the partition. File Explorer will show an even 100 GB.
Let’s walk through the common 100 GB example.
To create a 100 GB D: drive, enter 100 in the calculator’s “Desired partition size (GB)” field and click Calculate. Using the formula:
MB = (100 - 1) × 4 + 1024 × 100 = 99 × 4 + 102400 = 396 + 102400 = 102796.
The calculator shows “Size to enter (MB): 102796.”
Next, enter 102796 in the “Simple volume size in MB” field of the Windows New Simple Volume wizard. After formatting as NTFS, open This PC and the D: drive will display as 100.0 GB—without the trailing decimal.
If you enter 102400 directly, there is no compensation, and the result will be 99.9 GB—the frustrating missing 0.1 GB.
For comparison, here is a 50 GB example: G=50, MB = (50-1)×4 + 1024×50 = 49×4 + 51200 = 196 + 51200 = 51396. Enter 51396 to get 50.0 GB. With smaller partitions, the difference is easier to notice: entering 51200 for 50 GB displays 49.9 GB.
Create clean C: and D: drive sizes during setup
When building a PC or reinstalling Windows, you may want an exact 120 GB C: drive and a 300 GB D: drive. Use the calculator to get 122884 MB for 120 GB and 307236 MB for 300 GB, then enter them once—no more staring at 119.9 GB afterward.
Organize an external hard drive
Purchased a 2 TB external drive and want separate partitions for work, media, and backups? Calculate whole-number MB values for 700 GB, 800 GB, and the remaining space so every partition shows a clean, consistent capacity when connected to your computer.
Allocate virtual machine storage
When creating virtual disks in VMware or VirtualBox, you may still want Windows partitions inside the VM to display as whole numbers. Enter the calculator’s MB value during Windows setup in the virtual machine for cleaner disk properties later.
• The MB values from this calculator apply only to NTFS. Do not use them directly for FAT32 or exFAT, which require different values.
• This method does not apply to dynamic disks, spanned volumes, striped volumes, or other non-simple volumes because their metadata layouts differ.
• Your target partition size cannot exceed the drive’s available space. The calculator does not check your disk capacity, so confirm that enough space is available first.
• In Windows Setup, a small System Reserved or Recovery partition may use several MB. This does not prevent you from creating later whole-number partitions, but account for it when planning the total space.
• Advanced Format drives with 4K sectors may vary slightly. On most consumer drives, this formula has been tested to within 1 MB—enough to preserve a whole-number display.
Why does entering 102400 show 99.9 GB?
NTFS uses some space for file-system metadata, so the actual usable capacity is slightly below 102400 MB. Windows therefore rounds the displayed value down to 99.9 GB. The compensation formula adds that overhead in advance so the final usable capacity reaches an exact whole-number GB value.
Does this formula work with every version of Windows?
The NTFS compensation pattern has remained broadly consistent from Windows XP through Windows 11, and the formula has been extensively tested on Windows 7, 8, 10, and 11. In rare cases involving heavily modified systems or special configurations, there may be a 1 MB difference, but the display should still remain a whole number.
How do I create a whole-number FAT32 partition?
FAT32 has no single compensation formula because its file allocation table changes with partition size and formatting tools handle it differently. If you need a whole-number FAT32 partition, use a third-party formatting tool and fine-tune the size manually. This calculator does not currently provide a FAT32 algorithm.
Can I turn an existing non-integer partition into a whole-number partition?
Not directly by resizing it in Disk Management, because resizing preserves existing file-system metadata. Back up your data, delete the partition, recreate it with the calculator’s MB value, format it, and then restore your files.
Can I create a whole-number C: drive?
Yes. If you partition the drive manually during Windows installation, calculate the required MB value for C:, enter it, and install Windows normally. If Windows is already installed, changing C: usually requires repartitioning from a PE environment or bootable media. The process is more involved, but the principle is the same.
Try your own values in the calculator above—whether 100 GB, 250 GB, or 1 TB—and keep every partition looking clean and even.
