Check your disk space in three clicks
On Windows, right-click the drive in File Explorer and select Properties. A window opens showing a colored bar: the blue or purple section is what you are using, and the white section is what remains. The numbers below the bar tell you exactly how many gigabytes are full and how many are free.
On Mac, click the Apple menu, select About This Mac, then click the Storage tab. You see a horizontal bar with colored sections for different file types — Photos, Documents, Apps, and so on — plus a gray section for free space. The total capacity and available space appear at the bottom.
On Linux, open a terminal and type df -h to see all drives and their usage. The rightmost column shows the percentage full; the columns before it show total size and available space in gigabytes.
Key Takeaways
- Windows shows disk space in File Explorer Properties; Mac shows it in About This Mac under Storage; Linux users type df -h in a terminal.
- A drive that is more than 85 percent full slows down your system because the operating system needs free space to write temporary files.
- External drives and USB sticks use the same checking method as internal drives — right-click or open the storage settings.
- If you are running low, delete old downloads, empty the Recycle Bin or Trash, and move large files like videos to external storage before they fill your main drive.
Why the percentage matters more than the number
A drive with 50 gigabytes free sounds like plenty, but it depends on the total size. A 256-gigabyte drive with 50 gigabytes free is 80 percent full and will start to slow down. A 2-terabyte drive with 50 gigabytes free is 97 percent full and is in danger.
Your operating system needs breathing room. When a drive climbs above 85 percent full, Windows and Mac both struggle to write temporary files, cache data, and create the swap space they use when RAM runs out. You notice this as lag when opening programs, freezing when saving files, or crashes during updates. The slowdown is not because the drive is almost full — it is because the system cannot function properly without that buffer.
Check the percentage, not just the gigabytes. If you are above 85 percent, start moving or deleting files even if the number of free gigabytes seems reasonable.
Understanding what takes up the most space
On Windows, use Storage Sense to see what is eating your drive. Open Settings, go to System, then Storage. Click on any category — Apps, Documents, Downloads, Temporary files — and Windows shows you the largest items in that folder. This tells you whether your problem is old installers, video files, or something else.
On Mac, open About This Mac, click Storage, then click Manage. You see categories like Documents, Photos, and Backups, each showing how much space it uses. Click a category to drill down and see individual files.
On Linux, use du -sh * in your home directory to see which folders are largest, then navigate into the biggest ones and repeat the command to find the culprits.
Video files, photo libraries, and old backups are almost always the largest items. Once you know what is taking space, you can decide whether to delete it, move it to external storage, or compress it.
Moving files to external storage safely
Plug in your external drive and let your operating system recognize it. On Windows, open File Explorer and drag files from your internal drive to the external drive in the left sidebar. On Mac, drag files to the external drive icon on your desktop or in Finder. Do not cut and paste — drag and drop, which copies first and deletes only after the copy finishes.
Wait for the transfer to complete. On Windows, you see a progress bar; on Mac, the Finder window shows the transfer status. Do not unplug the drive until the bar reaches 100 percent and the window closes.
After the transfer finishes, check that the files exist on the external drive before you delete them from your internal drive. Open the external drive, navigate to the folder you just moved, and verify the files are there. Only then delete the originals from your computer.
Cleaning up without losing anything
Start with the safest deletions: your Downloads folder and Recycle Bin or Trash. On Windows, open File Explorer, click Downloads, and delete anything you no longer need — old installers, old documents, old screenshots. Then open the Recycle Bin and click Empty Recycle Bin. On Mac, empty the Trash by right-clicking the Trash icon in the dock and selecting Empty Trash.
Next, look for duplicate files and old backups. Many people have multiple copies of the same photo or document scattered across folders. Use your operating system's search to find files by date — search for files modified more than a year ago in folders you do not use regularly, and delete the ones you recognize as old versions or duplicates.
Temporary files and caches are safe to delete. On Windows, use Storage Sense to delete temporary files and old Windows installations. On Mac, you can safely delete the contents of the Downloads folder and empty the Trash. These files are meant to be temporary and will be recreated if needed.
Monitoring disk space over time
Check your disk space once a month, especially if you work with large files like videos, photos, or databases. Set a phone reminder to check on the first of each month. This habit catches problems early — a drive that is 70 percent full today might be 90 percent full in six weeks if you are not paying attention.
If you notice the percentage climbing faster than expected, something is creating large files in the background. On Windows, check if Windows Update is storing old installation files, or if your antivirus is keeping quarantined files. On Mac, check if Time Machine backups are taking up space, or if your photo library is syncing with iCloud. Identifying the source lets you fix it before the drive fills up.
External drives need the same attention. A backup drive that is 100 percent full cannot back up new files. Keep at least 10 percent of any drive free, whether it is your main system drive or an external backup.
Frequently Asked Questions
What does "used space" mean if I deleted files?
Deleted files still take up space until you empty the Recycle Bin or Trash. Until you do, they are counted as used space. Empty the Recycle Bin on Windows or Trash on Mac to actually free up that space. After you empty it, the used space number drops and the free space number rises.
Can I trust the free space number on an external drive?
Yes, but remember that external drives often have a small amount of space reserved for the file system itself. A 1-terabyte external drive might show 931 gigabytes of usable space because the rest is reserved. This is normal and not a sign of a problem.
What happens if my drive fills up completely?
Your system stops working properly. You cannot save files, install updates, or even restart sometimes. If this happens, delete files or move them to external storage when ready. If you cannot delete anything, you may need to boot from a recovery drive or external drive to access the system and free up space.
Should I delete system files to free up space?
No. Never delete files from Windows, System, or Library folders unless you are following specific instructions from a support article or technician. Deleting system files breaks your operating system. Stick to your Downloads, Documents, Pictures, and Videos folders, plus any files you created yourself.
Why does my drive show less free space than I expected after deleting files?
You may have deleted files but not emptied the Recycle Bin or Trash. You may also have temporary files, caches, or system updates taking up space. Use Storage Sense on Windows or the Manage button on Mac to see exactly what is using the space you thought you freed.