I have 2 SD cards (8 GB) I wrote my Wheezy image into one SD card (using Win32DiskImager) and I expanded the the disk space of the image on that card. then I used (Win32DiskImager) to read the Image and save it on my PC. Now I'm trying to write this image (the expanded one) on the other SD card, I got this error

"Not enough space on disk: Size 15730688 sectors Available: 15523840 sectors Sector size: 512"

I tried many SD cards I got the same error.

  • is this problem caused by expanding the image size to use all the specific SD card size?
  • do you suggest to expand the size manually to 7 GB even if the SD card size is 8 GB?
  • if i write (the expanded image) on the first SD card it works! why it didn't on the others?

Note: I used 2 software's to format the SD cards but non fixed the problem (SDFormatter) and (flashnul-1rc1).

2 Answers 2


The 8GB is only the guideline size of a card. Because of the nature of flash memory and management of dead cells there are slight variations in actual usable space.

This usable space will also decrease as the card gets older and older. With SSD's and SD cards like this it is a good idea to leave a small amount of space that is unused. I would say about 1% should be the safest for the life of the card.

So in theory 81.92mb on your 8gb (8192mb). Doing this on your master image will ensure that it will fit on any other 8GB.

In practice it is different. Take your 15730688 sectors and times it by 512 bytes. Divide by 1024 (number of bytes in megabyte) and again by 1042 to get Megabytes. That gives me 7681 mb. The other volume works out to 7580 mb. Slight difference but it causes so many issues. I would suggest going manually for 7500 mb.

It seems you used a card that has less errors and managed to expand to a size that is larger than other cards.

The same applies for hard drives but everything happens transparently. The firmware has spare space to mark bad sectors and move its physical location on the platter to the spare area automatically. Usually when you start to experience bad sectors that means it ran out of spare space for block relocation and that should be a warning sign to replace the Hard Drive.

  • 1
    Agree with you. To limit SD images to 7500 Megabytes with dd use bs=1m count=7500. Don't know if this can be done with Win32DiskImager. Commented Sep 27, 2013 at 9:34

This question is old but I think it's worth to add another answer:

There is a tool available called pishrink which shrinks an image to it's minimal size and will expand it to maximal size during boot. Just shrink your image, copy it to another sd card and you're done.

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