How to Completely Shrink the Docker Desktop Data Disk on Windows

This guide explains how to reduce the size of the Docker Desktop data disk on Windows when Docker is using the WSL 2 backend.

Docker Desktop stores its Linux filesystem inside a virtual hard disk file, usually called:

ext4.vhdx

The file can become very large over time because Docker images, containers, volumes, build cache, and deleted files may leave unused space inside the virtual disk.

Important: There are two different things involved:
Free space inside the Docker Linux filesystem.
The physical size of the ext4.vhdx file on Windows.
Running docker system prune only frees space inside Docker. To reduce the actual .vhdx file on Windows, the virtual disk must also be compacted.

1. Check the Current Size

First, check how large the Docker data disk is.

The file is commonly located somewhere similar to:

%LOCALAPPDATA%\Docker\wsl\disk\ext4.vhdx

You can open the directory with:

explorer "$env:LOCALAPPDATA\Docker\wsl\disk"

You should see something similar to:

ext4.vhdx

Check its size:

Get-Item "$env:LOCALAPPDATA\Docker\wsl\disk\ext4.vhdx" |
    Select-Object Name, Length

To display the size in GB:

$disk = Get-Item "$env:LOCALAPPDATA\Docker\wsl\disk\ext4.vhdx"
"{0:N2} GB" -f ($disk.Length / 1GB)

2. Clean Up Docker

Before compacting the virtual disk, remove everything that Docker no longer needs.

Warning: The following commands can delete unused Docker resources. Make sure you do not need unused images, stopped containers, networks, or volumes before proceeding.

Start with:

docker system df

This shows how much space Docker is currently using.

Example:

TYPE            TOTAL     ACTIVE    SIZE      RECLAIMABLE
Images          20        3         15GB      10GB
Containers      10        2         2GB       1GB
Local Volumes   15        5         20GB      12GB
Build Cache     ...                 ...       ...

3. Remove Unused Docker Resources

Remove stopped containers

docker container prune

Remove unused networks

docker network prune

Remove unused images

To remove dangling images:

docker image prune

To remove all images that are not currently used by a container:

docker image prune -a

Remove unused volumes

Be careful with this command:

docker volume prune

Volumes can contain important application data.

Only remove them if you are certain that the data is no longer required.

4. Clean Everything at Once

If you are certain that all unused Docker resources can be deleted, you can use:

docker system prune -a --volumes

This removes:

stopped containers
unused networks
unused images
build cache
unused volumes

Docker will ask for confirmation.

WARNING! This will remove:
...
Are you sure you want to continue? [y/N]

Enter:

Afterwards, check the result:

docker system df

5. Stop Docker Desktop Completely

Docker must not be using the virtual disk while it is being compacted.

First quit Docker Desktop.

You can do this from the Docker Desktop tray icon:

Docker Desktop
    -> Quit Docker Desktop

Then make sure Docker Desktop is no longer running.

You can also check:

Get-Process *docker* -ErrorAction SilentlyContinue

Ideally, no Docker Desktop processes should still be running.

6. Shut Down WSL Completely

Even after Docker Desktop has been closed, WSL may still have running distributions.

Run:

wsl --shutdown

This shuts down all running WSL 2 instances.

You can verify the state with:

wsl --list --verbose

The distributions should not be running.

For example:

  NAME              STATE           VERSION
* docker-desktop    Stopped         2

7. Make a Backup of `ext4.vhdx`

Before modifying the virtual disk, create a backup.

For example:

Copy-Item `
    "$env:LOCALAPPDATA\Docker\wsl\disk\ext4.vhdx" `
    "$env:USERPROFILE\Desktop\ext4-docker-backup.vhdx"

Depending on the size of the Docker disk, this can take a while.

Do not continue until the copy has completed successfully.

8. Compact the VHDX

There are multiple ways to compact the Docker VHDX.

The preferred Windows tool is diskpart.

Open PowerShell or Command Prompt as Administrator.

Start DiskPart:

diskpart

You should see:

Microsoft DiskPart version ...

DISKPART>

9. Select the Docker VHDX

Inside DiskPart, use:

select vdisk file="C:\Users\<USERNAME>\AppData\Local\Docker\wsl\disk\ext4.vhdx"

Replace:

<USERNAME>

with your Windows username.

For example:

select vdisk file="C:\Users\John\AppData\Local\Docker\wsl\disk\ext4.vhdx"

If your Windows installation is on another drive, use the corresponding path.

10. Compact the Virtual Disk

Once the VHDX has been selected, run:

compact vdisk

DiskPart should report something similar to:

100 percent completed

DiskPart successfully compacted the virtual disk file.

Then exit:

exit

11. Check the Result

Check the file size again:

$disk = Get-Item "$env:LOCALAPPDATA\Docker\wsl\disk\ext4.vhdx"
"{0:N2} GB" -f ($disk.Length / 1GB)

You can also check it in Explorer:

explorer "$env:LOCALAPPDATA\Docker\wsl\disk"

For example, before cleanup:

ext4.vhdx
Size: 80 GB

After cleanup and compaction:

ext4.vhdx
Size: 25 GB

The exact result depends on how much data was actually removed.

12. Start Docker Desktop Again

Start Docker Desktop normally.

Wait until Docker reports that it is running.

Then test:

docker version

And:

docker ps

Your containers, images, and volumes that were not removed should still be available.

13. Verify Docker Storage

Run:

docker system df

This lets you verify how much Docker is actually using.

You can also check the VHDX again:

$disk = Get-Item "$env:LOCALAPPDATA\Docker\wsl\disk\ext4.vhdx"
"{0:N2} GB" -f ($disk.Length / 1GB)

14. Optional: Check the VHDX Before and After

A convenient way to document the result is:

$disk = Get-Item "$env:LOCALAPPDATA\Docker\wsl\disk\ext4.vhdx"

[PSCustomObject]@{
    File = $disk.FullName
    SizeGB = [math]::Round($disk.Length / 1GB, 2)
}

Example output:

File                                                   SizeGB
----                                                   ------
C:\Users\John\AppData\Local\Docker\wsl\disk\ext4.vhdx  24.73

15. Complete Procedure

If you want the process as a short checklist:

1. Check current ext4.vhdx size
2. Check Docker storage
3. Remove unused Docker resources
4. Quit Docker Desktop
5. Run: wsl --shutdown
6. Back up ext4.vhdx
7. Start DiskPart as Administrator
8. select vdisk file="...\ext4.vhdx"
9. compact vdisk
10. exit
11. Start Docker Desktop
12. Verify Docker
13. Check the new ext4.vhdx size

16. Recommended Commands

The complete command sequence is approximately:

# Check Docker usage
docker system df

# Optional cleanup
docker system prune -a --volumes

# Shut down WSL
wsl --shutdown

Then, from an Administrator PowerShell/CMD:

diskpart

Inside DiskPart:

select vdisk file="C:\Users\<USERNAME>\AppData\Local\Docker\wsl\disk\ext4.vhdx"
compact vdisk
exit

Then start Docker Desktop again.

17. Important: `docker system prune` Is Not Enough

A common misconception is that:

docker system prune -a --volumes

will automatically make the ext4.vhdx file smaller.

It usually does not.

For example:

Before cleanup:

ext4.vhdx = 100 GB

Docker uses:
30 GB

Unused space:
70 GB

After Docker cleanup:

Docker uses:
30 GB

Unused space:
70 GB

ext4.vhdx:
still approximately 100 GB

After compacting the VHDX:

Docker uses:
30 GB

ext4.vhdx:
approximately 30–40 GB

The exact size depends on the filesystem layout and how much unused space can be reclaimed.

18. If `compact vdisk` Does Not Reduce the Size

If compact vdisk reports success but the file barely gets smaller, there may still be allocated blocks inside the Linux filesystem.

In that situation, first make sure Docker resources have actually been removed:

docker system df

Then shut everything down again:

wsl --shutdown

After that, retry:

diskpart
select vdisk file="C:\Users\<USERNAME>\AppData\Local\Docker\wsl\disk\ext4.vhdx"
compact vdisk
exit

If the VHDX still does not shrink sufficiently, an additional filesystem-level optimization may be necessary.

19. Important Difference: Dynamic VHDX vs. Maximum Size

The ext4.vhdx file is normally a dynamically expanding virtual disk.

This means:

Virtual disk capacity
        !=
Physical file size

For example:

Virtual capacity:    1 TB
Physical file size:  40 GB

does not mean that 1 TB is actually consuming 1 TB on your Windows drive.

The important value for Windows disk usage is the physical file size.

20. Do Not Delete `ext4.vhdx` Manually

Do not simply delete:

ext4.vhdx

unless you intentionally want to destroy the Docker Desktop WSL data.

Deleting the file can remove:

Docker images
Docker containers
Docker volumes
container filesystem data
Docker build cache
other Docker Desktop data

If you only want to reclaim disk space, use cleanup + VHDX compaction instead.

21. Recommended Safe Workflow

For production or otherwise important Docker environments, use this workflow:

                    ┌─────────────────────┐
                    │ Check Docker usage  │
                    └──────────┬──────────┘
                               │
                               ▼
                    ┌─────────────────────┐
                    │ Backup important    │
                    │ Docker volumes/data │
                    └──────────┬──────────┘
                               │
                               ▼
                    ┌─────────────────────┐
                    │ Remove unused Docker │
                    │ resources            │
                    └──────────┬──────────┘
                               │
                               ▼
                    ┌─────────────────────┐
                    │ Quit Docker Desktop │
                    └──────────┬──────────┘
                               │
                               ▼
                    ┌─────────────────────┐
                    │ wsl --shutdown     │
                    └──────────┬──────────┘
                               │
                               ▼
                    ┌─────────────────────┐
                    │ Compact ext4.vhdx  │
                    │ with DiskPart      │
                    └──────────┬──────────┘
                               │
                               ▼
                    ┌─────────────────────┐
                    │ Start Docker       │
                    │ Desktop again      │
                    └──────────┬──────────┘
                               │
                               ▼
                    ┌─────────────────────┐
                    │ Verify containers  │
                    │ and volumes        │
                    └─────────────────────┘

22. One-Liner to Find the Docker VHDX

If you are unsure where the Docker VHDX is located, try:

Get-ChildItem "$env:LOCALAPPDATA\Docker" -Filter *.vhdx -Recurse -ErrorAction SilentlyContinue |
    Select-Object FullName, Length

This searches the Docker directory for VHDX files.

23. Final Notes

The safest general approach is:

Docker cleanup
      ↓
Docker Desktop shutdown
      ↓
WSL shutdown
      ↓
VHDX backup
      ↓
DiskPart compact
      ↓
Docker Desktop restart
      ↓
Verification

How to Completely Shrink the Docker Desktop Data Disk on Windows

1. Check the Current Size

2. Clean Up Docker

3. Remove Unused Docker Resources

Remove stopped containers

Remove unused networks

Remove unused images

Remove unused volumes

4. Clean Everything at Once

5. Stop Docker Desktop Completely

6. Shut Down WSL Completely

7. Make a Backup of ext4.vhdx

8. Compact the VHDX

9. Select the Docker VHDX

10. Compact the Virtual Disk

11. Check the Result

12. Start Docker Desktop Again

13. Verify Docker Storage

14. Optional: Check the VHDX Before and After

15. Complete Procedure

16. Recommended Commands

17. Important: docker system prune Is Not Enough

18. If compact vdisk Does Not Reduce the Size

19. Important Difference: Dynamic VHDX vs. Maximum Size

20. Do Not Delete ext4.vhdx Manually

21. Recommended Safe Workflow

22. One-Liner to Find the Docker VHDX

23. Final Notes

7. Make a Backup of `ext4.vhdx`

17. Important: `docker system prune` Is Not Enough

18. If `compact vdisk` Does Not Reduce the Size

20. Do Not Delete `ext4.vhdx` Manually