I've seen a lot of sources from various websites saying more or less the same thing about this issue: that all you need to do is format the card to FAT32 for it to be read by a 3DS. However, I tried that and it didn't work, I was given the "3DS cannot detect SD card" error. So I did a little experimenting and I think I figured out why sometimes it won't work even if it's been formatted correctly.

I opened up the 8GB card that came with my 3DS and viewed the properties in a disk partitioning program I found, and I viewed the properties of the 64GB card after it had been formatted to FAT32. Then I did a little looking around on the forums here and found a thread that discussed this issue a little bit, and a user here posted links to some tools he had uploaded to filetrip. I used the first one, so I'll post the link here.

http://filetrip.net/ps3-downloads/tools-utilities/download-gui-fat32format-1-0-f22906.html

After using that tool, the SD card worked with my 3DS. So I looked at the properties in the same disk partitioning program, and there is only one difference I found that didn't pertain specifically to the size of the card.

It's the part I highlighted in yellow, the partition type. The 3DS seems to only detect cards with the 0C partition type. I was really fortunate to have found those utilities posted here, I can't find anything that can format a card with a specific partition type but that utility I used seems to do 0C by default. Please keep this in mind when you format your card to FAT32 and it still doesn't work, I'm like 80% sure that this is the only thing that would keep it from working, and it doesn't look like a lot of people knew about it so I thought it was worth posting here.

 

[gudenau]

Or just use DiskPart. :-P

cmd:

diskpart
list disk
select <disk>
clean
create partition primary
format fs=fat32 quick
exit

 

[piratesephiroth]

Use guiformat.

 

[Syphos]

Partition type 0x07 is either ExFAT or NTFS. The 3DS can't read that.
Partition 0x0C is LBA FAT32.

Never heard of Macrorit HDD Destroyer ah... sry I mean Macrorit Disk Partition "Expert".
Whatever this program does during formatting, it does it wrong.

You could have used a bootable Gparted or https://www.sdcard.org/downloads/formatter_4/
But I think the SD-formatter will format it back to exFAT instead.

 

[CZroe]

Or just use DiskPart. :-P

cmd:

diskpart
list disk
select <disk>
clean
create partition primary
format fs=fat32 quick
exit

The OP said "64GB and up," but DiskPart doesn't work for 64GB+ cards. "FORMAT FS=FAT32 QUICK" just gives you

0 percent completed

Virtual Disk Service error:
The volume size is too big.

 

[gudenau]

The OP said "64GB and up," but DiskPart doesn't work for 64GB+ cards. "FORMAT FS=FAT32 QUICK" just gives you

0 percent completed

Virtual Disk Service error:
The volume size is too big.

Did not know that!

 

[piratesephiroth]

I told you, guiformat is the best and easiest option.

 

[CZroe]

I told you, guiformat is the best and easiest option.

...and that's what I used. Thanks!

 

[vhaines]

or you can use sd formatter

 

[mangalodesh]

thank you all got a 128 micro sdxc sandisk class 10 uhs-1 working formatted and viewed with easus partition manager free fat32 gave hex 0D or OD can't go back now

 

[mangalodesh]

now its looking like OB or 0B hex