How to Partition a Hard Drive in Windows (Without Losing Data)

Affiliate Disclosure: This article may contain affiliate links. If you purchase through these links, we may earn a commission at no extra cost to you.

Splitting one physical drive into two or more partitions is one of the oldest tricks in PC housekeeping, and it still earns its keep. A separate partition keeps your personal files away from Windows system folders, makes a future reinstall far less stressful, and gives a shared family PC a tidy home for backups or media. Best of all, Windows ships with everything required in a built-in utility called Disk Management, so there is nothing to download and no third-party tool to trust with your data.

This walkthrough covers the full process on Windows 11 and Windows 10: shrinking an existing volume to carve out free space, creating a new partition inside that space, and formatting it so File Explorer can actually use it. Performed in that order, the procedure leaves your existing files exactly where they are — although a backup beforehand is still the smart play, for reasons covered below.

Before You Start: Back Up and Clear Some Space

Shrinking a volume is designed to be non-destructive, but any operation that rewrites the partition table carries a small amount of risk. Two quick preparations remove most of it:

1. Copy anything irreplaceable to a separate physical drive — our roundup of the best external backup drives covers reliable options if you don’t own one yet.
2. A volume can only shrink into space that data is not occupying, so free up disk space in Windows first if the drive is nearly full — the more empty room, the larger the partition you can create.
3. Restart the PC once before you begin. This clears pending Windows Update operations that can lock the disk and cause the shrink step to fail.

Step 1: Open Disk Management

1. Right-click the Start button and choose Disk Management from the menu (on both Windows 11 and 10 this shortcut menu also opens with Windows key + X).
2. Alternatively, press Windows key + R, type diskmgmt.msc and press Enter.
3. In the lower half of the window, find the disk you want to partition — disks are numbered Disk 0, Disk 1 and so on. Match it by its total size and existing drive letters before doing anything else.

Step 2: Shrink an Existing Volume

1. Right-click the volume you want to take space from — usually C: — and choose Shrink Volume.
2. Wait while Windows queries the volume for available shrink space. On a large, well-used drive this can take a minute.
3. In the box labeled Enter the amount of space to shrink in MB, type the size of the partition you want to create. Sizes are in megabytes: 1 GB is 1,024 MB, so a 100 GB partition means entering 102400.
4. Click Shrink. A black block labeled Unallocated appears next to the volume — that is your raw space for the new partition.

If Windows offers far less shrink room than the free space you actually have, unmovable system files (the page file, hibernation file and system restore snapshots) are usually sitting near the end of the volume. Microsoft’s Disk Management documentation notes these files cap how far a volume can shrink; temporarily disabling hibernation or system protection, then re-enabling them afterwards, typically unlocks the rest.

Step 3: Create and Format the New Partition

1. Right-click the Unallocated block and choose New Simple Volume.
2. In the wizard, accept the default size to use all of the unallocated space, or enter a smaller figure to leave room for another partition later.
3. Assign a drive letter — anything not already in use is fine.
4. On the format screen, keep NTFS and the default allocation unit size, give the volume a recognizable label such as Data, and leave Perform a quick format checked.
5. Click Finish. After a few seconds the new partition appears in File Explorer, ready for files.

NTFS is the right choice for a partition that will only ever live inside a Windows machine. If the drive is external and needs to move between computers, file-system choice matters a lot more — our guide to formatting an external hard drive explains when exFAT beats NTFS.

Extending or Deleting a Partition Later

1. To remove a partition, right-click it and choose Delete Volume. This erases everything on that partition (and only that partition), turning it back into unallocated space.
2. To grow a partition into adjacent unallocated space, right-click it and choose Extend Volume, then follow the wizard.
3. Note the catch: Extend Volume only works when the unallocated space sits immediately to the right of the partition in Disk Management’s map. If another partition sits between them, the built-in tool cannot jump over it.

If the real problem is that the whole drive is too small rather than badly divided, repartitioning won’t fix it — cloning the drive to a larger SSD moves Windows, your files and your partitions in one operation.

Common Mistakes to Avoid

Treating a second partition as a backup. Both partitions live on the same physical drive, so a mechanical failure or dead controller takes them down together. A partition organizes data; only a copy on separate hardware protects it.

Shrinking the Windows volume too far. Leave C: at least 20 percent free after the shrink. A nearly full system volume slows updates, and Windows needs headroom for temporary files and the page file.

Working on the wrong disk. Disk numbers in Disk Management don’t always match the order drives were installed. Confirm the size and drive letters twice before shrinking or deleting anything.

Partitioning a failing drive. Resizing stresses a drive with pending sector reallocations. If the disk is old or has been acting up, check the drive’s health first and replace it instead of reorganizing it.

Frequently asked questions