How to Check File Hash with PowerShell

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In this tutorial, we will show how to verify file integrity in Windows using PowerShell: calculate checksums with Get-FileHash, compare directories by hash, and detect duplicate or corrupted files.

What Is a File Hash and Why It Matters

To verify that large files, distros, or ISO images are downloaded completely, without errors, and were not modified during transition, you can check their hash. Unlike a file name or extension, a file hash (also known as a checksum) is a unique value that depends solely on the content of the file. The resulting hash can be compared to the original to verify the file’s integrity and authenticity.

In Windows, you can compute the hash value of any file without using third-party tools. You can use either the CertUtil.exe console command or the Get-FileHash PowerShell cmdlet.

How to Calculate File Hash Using PowerShell

Open the PowerShell console and specify the full path to the file whose hash you want to calculate:

Get-FileHash F:\ISO\Win_11_25H2.ISO

The SHA256 algorithm is used by default to calculate the file hash. After a while, the command will output the hash of the specified file to the screen. The time required to calculate a file hash with the Get-FileHash command depends on the file’s size and the hashing algorithm used.

If the file’s contents change by even one character, its hash will differ the next time you check.

The Get-FileHash cmdlet lets you specify the specific cryptographic algorithm used to calculate the hash.

Supported Hashing Algorithms in PowerShell

Commonly available algorithms include:

• SHA1
• SHA256 (default)
• SHA384
• SHA512
• MD5
• MACTripleDES
• RIPEMD160

To use a specific cryptographic hash function, specify it with the -Algorithm argument:

Get-FileHash -Algorithm MD5 F:\ISO\Win_11_25H2.ISO

Note. Although MD5 is the fastest algorithm for obtaining a file checksum, it is now considered obsolete and insecure. The SHA-256 algorithm offers good performance and a low probability of collision (when two different files have the same checksum).

How to Find Duplicate Files by Hash

With PowerShell, you can quickly find duplicate files in a directory based on their content, regardless of file names or extensions:

Get-ChildItem -Recurse -File "F:\ISO" |
Get-FileHash |
Group-Object -Property Hash |
Where-Object { $_.Count -gt 1 } |
ForEach-Object { $_.Group | Select-Object Path, Hash }

In this case, we found two ISO image files with the same content.

How to Compare Directory Contents by File Hash

It is often necessary to compare the contents of two directories to ensure they are identical, such as after backing up files. This helps to ensure the backup is consistent. The easiest way to compare directory contents is by calculating and comparing the hashes of the files within them.

$SourceFolder = "C:\Data"

$TargetFolder = "F:\Data"

$FirstFolder = Get-ChildItem $SourceFolder -File -Recurse |
Select-Object *,
@{
Name="RelativePath"
Expression={$_.FullName.Substring($SourceFolder.Length)}
},
@{
Name="Hash"
Expression={(Get-FileHash $_.FullName).Hash}
}

$SecondFolder = Get-ChildItem $TargetFolder -File -Recurse |
Select-Object *,
@{
Name="RelativePath"
Expression={$_.FullName.Substring($TargetFolder.Length)}
},
@{
Name="Hash"
Expression={(Get-FileHash $_.FullName).Hash}
}

Compare-Object `
-ReferenceObject $FirstFolder `
-DifferenceObject $SecondFolder `
-Property RelativePath,Hash

This PowerShell script calculates hashes for all files in the source and destination folders, displaying only those with differing contents.

How to Verify File Integrity Against a Reference Checksum

Many developers publish checksums of their source files on their official websites to allow users to verify the file’s integrity. The user can calculate the file’s checksum and compare it with the reference value to verify the file’s integrity and confirm it has not been corrupted, damaged, or tampered with during download.

So, another common use case is obtaining a file’s hash value and comparing it to the expected one.

$isoFile = "F:\ISO\Win_11_25H2.ISO"

$hashFile = "F:\ISO\Win_11_25H2.hash"

$computedHash = (Get-FileHash $isoFile).Hash.Trim()

$expectedHash = (Get-Content $hashFile).Trim()

$computedHash -eq $expectedHash

This script will return True if the file hash matches the reference value and False if they differ. This example assumes the hash file contains only the checksum value.