Find Windows disks below a free-space threshold

Script 3 min read Windows PowerShell 5.1 and PowerShell 7

Written and tested by Dhrub Bharali · Updated 02 October 2026

Report fixed local disks with less than 20 GiB free, showing free and total capacity as numeric values.

Example reviewed 1 October 2026 · Illustrative output · Not a live system check

The script

$MinimumFreeBytes = 20GB
Get-CimInstance Win32_LogicalDisk -Filter 'DriveType=3' -ErrorAction Stop |
    Where-Object FreeSpace -lt $MinimumFreeBytes |
    Select-Object DeviceID,
        @{Name='FreeGB'; Expression={[math]::Round($_.FreeSpace / 1GB, 1)}},
        @{Name='SizeGB'; Expression={[math]::Round($_.Size / 1GB, 1)}}

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$MinimumFreeBytes = 20GB
Get-CimInstance Win32_LogicalDisk -Filter 'DriveType=3' -ErrorAction Stop |
    Where-Object FreeSpace -lt $MinimumFreeBytes |
    Select-Object DeviceID,
        @{Name='FreeGB'; Expression={[math]::Round($_.FreeSpace / 1GB, 1)}},
        @{Name='SizeGB'; Expression={[math]::Round($_.Size / 1GB, 1)}}

Inspection only — no command has run.

Show reference output

Fictional reference snapshot · 03 October 2026, 09:00 UTC. This is an example result, not a check of your systems.

DeviceID  FreeGB  SizeGB
--------  ------  ------
C:        12.4    128

Inspect this example’s structure

Read the command and its supplied arguments. This example requires real PowerShell or its module; this diagram does not execute it.

$MinimumFreeBytes = 20GB
Get-CimInstance Win32_LogicalDisk -Filter 'DriveType=3' -ErrorAction Stop |
    Where-Object FreeSpace -lt $MinimumFreeBytes |
    Select-Object DeviceID,
        @{Name='FreeGB'; Expression={[math]::Round($_.FreeSpace / 1GB, 1)}},
        @{Name='SizeGB'; Expression={[math]::Round($_.Size / 1GB, 1)}}

Stage 1$MinimumFreeBytesPositional values or no named parameters
Stage 2Where-Object-lt
Stage 3Select-ObjectPositional values or no named parameters

Illustrative output

This example shows the expected shape for fictional data. Your values and formatting will differ.

DeviceID  FreeGB  SizeGB
C:        12.4    476.1

How it works

The CIM filter selects fixed disks. Where-Object applies the 20GB threshold in bytes before rounding for display. The FreeGB and SizeGB labels use the common PowerShell convention; their divisors are binary gigabytes (GiB).

Before you run it

Windows and permission to query Win32_LogicalDisk are required. Choose a threshold suitable for the workload; a single absolute limit does not replace percentage-free or growth-rate checks.

Check the result

Confirm the selected drive and compare raw FreeSpace with the threshold. Inspect trends and application requirements before planning cleanup. This report does not delete files.

If nothing is returned

If the query succeeded, no returned fixed local disk had less than 20 GiB free. Network shares and other excluded storage still need their own checks.

Practise the underlying skill

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Read the primary Microsoft documentation

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