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Can anyone tell what are the dimensions and/or volume for a 3.5-inch floppy disk?

I am doing a presentation and want to make a visual on how many floppy disks are required to save 200 GB (73662 floppy disks I believe).

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    How exactly did you came up with a value of 73662 floppy disks for 200 GB?
    – Justme
    Dec 19, 2022 at 13:50
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    I would assume it has been calculated using the uncommon extended-density format (2880 KiB), but yes, I have been wondering too.
    – user3840170
    Dec 19, 2022 at 14:03
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    @Eight-BitGuru What a strange definition of a gigabyte.
    – user3840170
    Dec 19, 2022 at 20:28
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    @Eight-BitGuru 200 binary gigabyte (gibibyte) is 200*1024^3 = 214,748,364,800 bytes. A "1.44" floppy is 1,440 KiB=1,474,560 bytes, so 200 gibibytes is 145,636 floppies. If we take 200 decimal gigabytes, we have 200,000,000,000 bytes, and 135,634 floppies.
    – user71659
    Dec 19, 2022 at 22:40
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    You might want to check this video: youtu.be/J-K2yeQylCk
    – Gerardo Furtado
    Dec 20, 2022 at 4:02

3 Answers 3

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A standard 3.5" floppy disk (ANSI X3.137 or ANSI X3.171 size) is physically 90mm x 94mm x 3.3 mm, with a 85.80 mm diameter magnetic disk in the cartridge.

This is the same whether the media is DD, HD or ED inside - so 720k and 2.88M DOS formats are the same physical size.

I believe, but cannot find references to verify this, that the LS-240 media (240 MB disks) was the same physical dimensions as the ANSI standard floppy.

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    The wikipedia page for the LS-120 and LS-240 talks about being able to use standard 3.5" disks in the LS- drive, and that the LS- disks expose a fake FAT12 filesystem when put in a standard 3.5" drive. That would imply that they're the same size.
    – Roger Lipscombe
    Dec 20, 2022 at 14:52
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The ECMA-147 standard (and, I am told, the ANSI X3.137 standard too) defines the dimensions of a ‘3.5 inch’ floppy disk as 90 mm × 94 mm × 3.3 mm, which multiplies up to a volume of 27918 mm³ = 27.918 ml (though this is arguably imprecise as it includes the volume of all the notches that, strictly speaking, aren’t part of the floppy disk cassette).

Storing 200 GB of data on floppy disks in probably the most common high-density PC format (1440 KiB each) would require ⌈200 × 1000³ ÷ (1440 × 1024)⌉ = 135 634 floppy disks, so your figure appears to be about two times too small. But even that doesn’t take into account file system overhead; assuming each floppy contains a FAT12 file system with standard sector reservations (1 boot sector, 14 sectors for directory entries, 2 FATs of 9 sectors each) containing a single file, you end up with ⌈200 × 1000³ ÷ (2847 [sectors] × 512 [bytes per sector])⌉ = 137 206 disks. If it’s just for illustrative purposes the difference probably doesn’t matter too much, as it’s still roughly the same order of magnitude, but it would be a quite significant one if storing all that data was actually attempted.

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    So basically a stack of floppies about as tall as the Petronas Towers (just mere 2.75 tons of them if we go at 20 grams a piece).
    – Dan Mašek
    Dec 19, 2022 at 23:21
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    "arguably imprecise as it includes the volume of all the notches" Actually, this is precisely the right way to calculate the volume in this context. You can't exactly recover the space used by the notches for packing the floppies tighter, so the dead space needs to be included.
    – nitro2k01
    Dec 20, 2022 at 3:35
  • Excluding the notches is a bit like excluding the internal space between the disk and the corners of the case.
    – Toby Speight
    Dec 21, 2022 at 13:47
  • I was thinking mostly of the cut corner. Perhaps on a large enough scale, that might actually count for something.
    – user3840170
    Dec 21, 2022 at 14:48
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Other stats for your 73,662 floppies:

  • They would weigh roughly 1326 kg. This is about the same as a Mini Cooper S car.

  • The labels on their backing paper would cover an area of almost 325 m² (assuming Memorex labels, which came on a 76 × 58 mm sheet): enough to cover the floor of the US White House's Oval Office 4¼ labels deep.

  • A roll of labels to label every one would be 4.27 km long (assuming 58 mm per label)

  • If packed in boxes of 10 like you got from Memorex, you'd need 7367 boxes, each 94 × 45 × 97 mm. This would cover a standard shipping skid/pallet (1.2 × 1 × 0.162 m) to a height of just over 2.7 m. This wouldn't fit inside a standard sea can / shipping container: they only have a headroom of 2.38 m.

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  • I'm aware that the boxes of floppies would probably crush if stacked that high on a palette unless packed in outers. I leave that as Somebody Else's Problem
    – scruss
    Dec 21, 2022 at 14:53

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