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Reformat your USB flash drive to access its full storage capacity

Reformat your USB flash drive to access its full storage capacity

Reclaim lost storage space by getting rid of the hidden files and junk that accumulates on your USB flash drive over time.

Nearly everyone has a USB flash drive for portable data storage nowadays, and for the most part they work with almost any computer effortlessly. Sometimes, though, a particular brand or model will not play nice when you frequently connect it to both Windows and Mac systems. Both operating systems routinely create hidden files, and items you thought you deleted may still be there after all. After a while you might not be able to take full advantage of your flash drive’s full capacity, because these unwanted files are taking up space.

For example, if I have a 4GB drive and I only have about 1.5GB of usable data on it, I might only have about 750MB of free space left. Of course, this doesn’t quite add up to my flash drive’s full size so clearly something I can’t see is there taking up space.

The first and most common way to fix this problem is to ensure your Trash has been emptied in Mac OS X. When you delete a file from your USB flash drive on a Mac, it goes to a special hidden directory on the drive and stays there until you empty the Trash. You must do this while your storage device is connected.

If the previous method doesn’t help you, the next one certainly will. Follow these steps to erase and reformat your drive:

1.) If you have any important data on your USB flash drive, make sure you temporarily copy the files to your Mac’s desktop.

2.) Open up Disk Utility (Applications > Utilities) and select your flash drive on the list to the left.

Reformat your USB flash drive to access its full storage capacity

3.) Choose the Erase tab near the top of the window and select MS-DOS (FAT) from the Volume Format drop-down menu. This is required if you want your drive to be Windows-compatible.

4.) Give your drive a name (keep it short with no special characters).

5.) Finally, press the Erase… button and your drive will be wiped clean.

This process will give you access to your USB flash drive’s full formatted storage capacity. If you backed up the drive’s data to your desktop, you can copy it back and use it just like before — with more free space!

115 Comments Have Been Posted (Leave Your Response)

Thanks! This was very helpful.

This Was SOOOOOO Helpful

I’ve had my macbook for about 7 or 8 months, and i still know very little about it, because i haven’t taken the time to explore it and what not

But this was sooo easy, and soooooo helpful

thank you SO much!

Thank you so much for this post!! It was extremely easy to follow and worked like a charm!! :) I can use my flash drive again!! :)


Thanks for the walk-through. I brought USB drives infected with malware home from work and reformatted them for Mac, just to make sure the malware was really really dead. Then, I took them back to work to be reformatted on the healed PCs.

Wow, Thank you so much! I had no idea about any of this! I routinely go between my Mac and clients’ PCs, so I was down to 4Kb of space left! On a seemingly empty USB!

Thanks again!

Thanks a bunch!

Thank you so much, I was convinced my flash drive was as good as dead, but this has solved the problem!


Awesome tip! It was making me so frustrated when I couldn’t save all my files although it looked like there was enough space.

Thanks! Worked like a charm!!!!! Sherri

Thanks! that totally worked! and was super easy. my 2gig drive wouldn’t let me put 10mb files onto it even though it had plenty of room (supposedly). I did your erase tasks and it works like a charm.

THANKS!!!! super-easy haha

Man, that just saved my butt. Had a presentation to give in front of 45 stakeholders and saw that my thumb drive had run out of space. So happy that it worked. Thank you.

Thank you!!! veryyy helpful especially for a beginner

I have done that a couple of times now in ms dos mode and everything but every time I try and use it with a pc it says that the drive needs to be reformatted and then when I reformat it on the pc it only formats 200mb of the drive.

hei thanks for the help! but, why when i put a file on my flashdisk and i delete it, it wont change the free capacity. how could this thing happen??

u just saved the day!
(and my boyfriend thought i broke it.. :P)

Thank you!!! I have about 3 flash drives laying around that I thought I couldn’t use anymore because they were “full”. Yay thanks!

oh my gosh, thank you so, so much. i love you. you just saved my weekend.

Thank you!!!,it was very helpful.

acharya Shrikrishna
January 5th, 2011, 6:48 AM

i have a macbook5,2 snow leopard and am unable to open Disc utilities to format a usb pen drive. pray help me.
thank you,

I’ve just erased a 2 Gb Kingston Data Traveller Flash Drive. Message came up:

“Disk Erase failed

POSIX reports: The operation couldn’t be completed.
Cannot allocate memory”

Removed Flash drive. No disk image.

Shows up on Disk Utility but cannot reformat.

Should I buy a new Flash drive?

you are the best, saved my life!

Thank you so much! I was on the verge of crushing and throwing away my USB as it has been acting up and allowing me to save less and less every time I tried to use it .. after following this, it works like new and I finally have full availability again!
GREAT walk through!

I use my flash drive between my macbook and my PC from work, but after a while i notice that my flash drive saids that no space was available still been empty, i used the disk utility option and worked perfect… but after usuing it i notice that i had less space in my flash drive… went from 16GB to 15.57GB, any idea why this happens?

hiya, and thanks for this – very easy to follow.

i have a new 16GB flash drive, unused, but my Mac reckons there is only 14.3GB free space on it. Does that means the files that arrived on the drive from the manufacturer are taking up over 1GB of space?!
This seems crazy. How can I tell which of the files I really need to keep on there so the drive will work, and hat I can scrap straight away?



I happened to stumble across this whilst trying to solve another issue, amazing help! Been wondering why my flash drive has nothing in it yet was empty :)

When I erase the flash drive, it still says there are 9 folders, 38 files and 6 MB used.
It says there is a Partition map but when I look at it, there is only 1 partition of the same capacity as the flash drive.
What’s going on, do you know?
I emptied the trash, again, and the file count went up to 40. I repaired the disk and the file count went up to 43. It must be keeping a log. I erased, again, and am back down to 38 files.
I can’t see any folders or files on the disk.

Thanks for any help you can give me.

You’re awesome thank you very much

My 1GB flash drive mysteriously dropped to a useless 267KB device. No online advice made sense to this non-Geek Mac user until I came across your Web page. I tried your first suggestion to empty the trash while the flash drive is connected to the computer. It was the simplest of all the troubleshooting schemes–but it worked instantly, restoring my device to its full capacity.
Thanks a whole lot, Ant.

Thank you so much! This was so helpful and I’m glad I came across this site! :)

Thanks so much! This was EXACTLY the information I needed. AWESOME!!!

aah, thank you ive been bugged for soo long. Thanks and ive owned my mac for over a year now and know the least about it D:

thank you so much, extremely helpful =]

thank you s much…i need leave comments when using internet help but this was amazingly easy and useful!

sebastian noguera
October 3rd, 2011, 8:11 PM

Thank you soo much!!! so helpfull

Thanks a bunch worked like a charm!

THANKS SOOOOOO MUCH! i had the exact problem you described! a 4gb flash drive but it said i only had 7.5 mb available even though it was completely empty. followed your steps and now its perfect. thanks again!

Thanks a Ton…it stopped me from buying a new pen drive…Thanks Once Again!:-)

My trash had not been emptied! haha thanks for the post

oh my God, you’re a genius.

Thank you! My OS is Ubuntu 11.10 and this solution worked for me!

Kristin Russell
May 11th, 2012, 7:02 AM

I have to do this everytime i want to put something on my memory stick, anyone know why?

U SAVED MY LIFE!!!!!!!!!!!!!!!

Thank you so much, it makes a lot of sense now!

Thanks! Was super helpful!!!

Thank you so much! Had only 1.15gb available on 8gb flash drive, emptied trash and, bam, 7.96gb. Thanks a lot

oh i am so grateful. thank you for posting! i had no idea where to begin :-D

thank you very much this has helped me sooooooo much

This was helpful, as my two pen drives said they are full when nothing was in, so emptied trash and now pen drive has its original capacity. thanks

so grateful and thankful i found this!! thanks a lot!

Thanks. After all this time, your advice is still helping.

Thank you! Emptying trash fixed problem with 8gb. Xbox flash!

excellent advice on an easy fix! thanks heaps!!

Thanks! This was incredibly correct, fast, and easy to follow. I appreciated it.


Along with all the others – A BIG THANKS! Can’t figure out though why this kind of information isn’t more readily/publicly available by the flash drive manufacturers or Mac itself. You’ve SO helped us all. So simple yet totally effective for my latest scan disc flash drive on my Mac.

The original 8GB Toshiba flash drives unfortunately didn’t respond to these fixes. Seem to be stuck with a partition and only 4mb of space left, but no files on them. Any other suggestions readers?

i just want to say that this was helpful… but i feel stupid now because all i had to do was empty my trash. honestly i had the biggest face palm ever. any thanks a lot :D

Thanks for this, it was so so helpful i like it. Thanks

THANK YOU!!! It was driving me crazy that it was showing the wrong capacity. AWESOME! ;)


omg! thank you so much for a moment in my life i thought that i would have to throw it away and buy a new flashdrive! thank you if i had money to spend i would donate some to you thnks so much!

Thanks buddy, this was very helpful.

Thanks a lot mate, life saver.

Wow. Thanks. Turns out my flash drive had over 330 hidden files, including a website, pictures, and several powerpoints… no wonder I had no space! Thank you again. :)

Thank you so much!!! I thought I was doomed when the flash drive still didn’t have any space left after emptying the trash on my mac. The disk utilities step worked!

Like everyone else said, super helpful!

Thank you SOOOOO much!!!!!!!!!!

That was so helpful. Such a simple task but I have a number of flah drives sitting around empty claiming they have no storage on them…jerks. Not any more!!!

It worked straight away! Thankyou so much! Now i can stop buying new usb’s and just fix my old ones. Its much appreciated


I configured my 4GB SanDisk to my Xbox360 but when I plugged it back in it said I only had 47MB left.

The Disk Utility worked perfectly.
Thank you!!

I’ve tried to do this, but I can’t see where is says ‘erase’. Where is that exactly?


I also have windows running my my Mac and did all the above and still could not get my 4.5gb video onto my flash drive. Not enough space. After an hour of searching the stick was formatted to FAT or something like that which will only allow a file up to a max of 4gb, I had to go into windows and re format to NTFS and now it is fine. Why it allows only up to 4gb is beyond me !!!!!

Thank you thank you thank you! All I needed to do was empty my trash! I was getting so frustrated, you’re a hero!

Thanks! 10/10, this worked!

Thank u so much, this was very helpful!!

Brilliant, still learning stuff about the MAC.

i tried to format an exfat 64 gb flash drive, it does not want to highlight the format. i see the flash drive on disk utility even if i try do delete a file it won’t go to the trash. please help what can i do to format it. the flash drive used to be ntfs and it has been formatted to exfat but the disk utility won’t allow me to format it again. what can i do?.

fantastic worked wonderfully thank you

This was SUPER BLESSING, I spent good money on this and thought i was gonna have to trash it not to mention the “not having a jumpdrive struggle”…..THANKS ANT

Thanks so much, very helpful!

I have researched this question previously and it took me about an hour to come to a resolution which was to reformat it in windows? I have just conducted another search thinking surely I don’t have to do this on a Windows computer? Thank you very much for your answer!!!!! Worked fine :)

Thank youuu so much i have like 5 USBs and theyre all full but now its nott.. Thankss!!

Thanks so much. This worked perfectly!!!

Thank you very much! Simple, quick and super useful fix..worked just like you described..and my problem was resolved in under 2 minutes..

Thank you so much! This was so helpful and easy!

hey thanks a lot really helpful

I pulled a thumb drive out of my Mac but did not hit the eject button first. Now the Mac won’t recognize the thumb drive. How do I get it to run again?

After i clicked the erase button, a message appeared saying :

‘Disk Erase failed

Disk Erase failed with the error:

Unable to write to the last block of the device.’

What should I do? I can’t reformat it..

AWESOME! Thank you so much!!

Excellent solution many thanks

grateful, thanks!

awesome, thanks

Thankyou very helpful. Wish I had found this hours and hours ago!

I too, found I had a couple of USB drives that showed empty but had almost zero capacity. I erased them via Utilities. Fine. (didn’t get to the part about emptying Trash….doh.
Now my iMac does not show the drives in Finder (although I get a reminder to eject msg when I remove it).
The drive is recognized on my Macbook.
So now I can’t use my memory sticks in my iMac.
How can I get the iMac to recognise the sticks?

Whoever you are, thank you so much. You are very smart! You made me smile with satisfaction.

Thanks…worked perfectly!

Awesome. Works like a champ!

You are the Boss of msdos

Thank you so much!!

Thank you very helpful

This was the most helpful and simplest page I could find! It worked perfectly and saved me from having a lot of trouble in a photography class. Thank you so much!

Thank you so much!!!! I’ve been looking for ways to clean out my USB drive and this method has been the best.

You are the man!!!! Yahooo..brought back 25gigs by the trashing method!!!

I tried so many other things before I found this and it worked perfectly! Thank you SO much!

So simple I never would have thought of this. MANY THANKS!

THANK YOU SOOOOOO MUCH… I was literally about to shoot myself!

I didn’t think that deleting your trash thing would work but it does! THANKYOU!!! My 5 year old USB had only 436 MB out of 4 GB

How can i get rid of the name for example yours says 3.9 GB JetFlash. is there a way to get rid of this?

Well…I’m trying to download a mod for gta 5 online with my macbook and it said zero kb left I will try this when I wake up and tell you if it works!

my pendrive shows 0 bytes storage capacity how i recover it , i do all possible solution for my pendrive but i can’t get my storage capacity.

Thanks man! this is very helpful

Thank you so much. Trash bin emptying worked!!!!!

Thank you so much, you’re a lifesaver…I had a whole stack of flash drives I thought were unusable!

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