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What is the weight of a 3.5 inch floppy disk and was the weight ever standardized?

a bunch of 3.5inch floppy disks

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  • 19
    Why do you think that the mass might be standardised, especially of the whole package? I could understand some standardisation for the disk itself (or more specifically its moment of inertia about the spindle axis), but even that seems unlikely, as drives will just take longer to spin up heavier disks than lighter ones. It's actually a differentiating feature (build quality against speed against cost) of different brands.
    – Toby Speight
    Jun 15, 2021 at 15:01
  • 4
    What’s more, there’s quite a lot of scope for variation: the rotating disk itself probably won’t vary much, but the rigid package can, the larger disk at the centre also can, metal shutters weigh more than plastic shutters, different types of spring can be used, and some disks even had protective coating inside the rigid package which would add (a little) weight.
    – Stephen Kitt
    Jun 15, 2021 at 15:14
  • 7
    Some disks hold more data than others. Therefore it is logical to conclude that Double Density disks must weigh more than Single Density disks, right? ;^)
    – Geo...
    Jun 15, 2021 at 15:47
  • 16
    Depends: European or African?
    – Carl Witthoft
    Jun 16, 2021 at 12:49
  • 3
    @ReversedEngineer, That depends on whether you think that "disk" refers to the circular piece of coated mylar film that is contained within the assembly, or whether you think it refers to the entire assembly. The mylar film certainly is floppy (Don't ask me how I know!)
    – Solomon Slow
    Jun 16, 2021 at 15:38

2 Answers 2

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The short answer / TLDR: One 3.5-inch floppy disk weighs between 15 - 25 grams. The average (mean) weight of one 3.5-inch floppy disk is 18 grams, the median is 17 gram. Of that weight 75% is estimated to consist of the plastic housing and paper ring only, 14% for a metal shutter and 11% for the hub.

The data

Below you'll find the data (in semicolon CSV format) as requested in the comments. It contains the brand and production country if available, whether the disk contained a paper label and what type of disk 3.5-inch disk it was (HD or DD).

Brand;ProductionCountry;LabelPasted;HD/DD;Grams
Unknown;Unknown;Yes;HD;18
Unknown;Unknown;Yes;HD;19
Verbatim;Unknown;No;HD;18
Unknown;Germany;Yes;HD;20
Unknown;Unknown;Yes;HD;21
Unknown;Germany;Yes;DD;21
Unknown;Unknown;No;HD;16
MCN;Unknown;Yes;DD;21
BASF;Unknown;Yes;HD;19
Unknown;Unknown;Yes;HD;18
Unknown;Japan;No;HD;21
Unknown;Germany;Yes;HD;19
Unknown;Unknown;Yes;HD;19
Unknown;Germany;Yes;HD;25
Unknown;Germany;Yes;HD;21
Unknown;Unknown;Yes;HD;18
Unknown;Germany;Yes;HD;20
3M;Unknown;No;HD;21
Unknown;Unknown;Yes;HD;20
Unknown;Germany;Yes;DD;21
Unknown;Germany;Yes;DD;21
3M;Unknown;Yes;DD;20
3M;Unknown;Yes;DD;22
3M;Unknown;Yes;DD;22
3M;Unknown;Yes;DD;22
3M;Unknown;Yes;DD;22
3M;Unknown;Yes;DD;22
3M;Unknown;Yes;DD;22
3M;Unknown;Yes;DD;23
Unknown;Germany;Yes;DD;21
Unknown;Germany;Yes;DD;21
Unknown;Germany;Yes;DD;20
Maxell;Japan;Yes;DD;21
Maxell;Japan;Yes;DD;22
Maxell;Japan;Yes;DD;21
Fujifilm;Germany;Yes;DD;19
Nashua;Japan;Yes;DD;21
Nashua;Japan;Yes;DD;22
Nashua;Japan;Yes;DD;21
Nashua;Japan;Yes;DD;22
Nashua;Japan;Yes;DD;21
Nashua;Japan;Yes;DD;22
Unknown;U.S.A.;No;DD;21
Unknown;Unknown;Yes;DD;21
Unknown;Unknown;Yes;DD;22
Unknown;Unknown;Yes;DD;21
Unknown;Unknown;Yes;DD;22
MCN;Unknown;Yes;DD;21
MCN;Unknown;Yes;DD;20
INMAC;Unknown;Yes;DD;21
Unknown;Unknown;Yes;DD;21
BASF;Unknown;Yes;DD;23
Unknown;Unknown;Yes;DD;21
Unknown;Unknown;Yes;DD;22
Unknown;Unknown;Yes;DD;22
Unknown;Germany;Yes;DD;19
Unknown;E.C.;Yes;DD;17
3M;Unknown;No;HD;21
Unknown;Unknown;No;HD;21
Unknown;E.C.;No;HD;17
Unknown;Unknown;No;HD;20
Unknown;E.C.;No;HD;20
Unknown;Germany;No;HD;17
Unknown;Germany;No;HD;17
Unknown;Germany;No;HD;17
Unknown;Unknown;No;HD;18
Unknown;Unknown;No;HD;20
Unknown;Unknown;No;HD;21
Unknown;Unknown;No;HD;17
Unknown;Germany;No;HD;17
Unknown;Unknown;No;HD;18
Unknown;E.C.;No;HD;17
Unknown;Unknown;No;HD;17
Unknown;Unknown;No;HD;19
Unknown;E.C.;No;HD;17
Unknown;Unknown;No;HD;17
Unknown;Unknown;No;HD;17
Unknown;Unknown;No;HD;17
Unknown;Unknown;No;HD;19
Unknown;Unknown;No;HD;19
Unknown;Unknown;No;HD;20
Unknown;Unknown;No;HD;20
Unknown;Unknown;No;HD;19
Unknown;Unknown;No;HD;20
Unknown;Unknown;No;HD;19
Unknown;Unknown;No;HD;19
Unknown;Unknown;No;HD;20
Unknown;Unknown;No;HD;18
Unknown;Unknown;No;HD;20
Unknown;Unknown;No;HD;20
Unknown;Unknown;No;HD;19
Unknown;Unknown;No;HD;21
Unknown;Unknown;No;HD;19
Unknown;Unknown;No;HD;20
Unknown;Unknown;No;HD;18
Unknown;Japan;No;HD;21
Unknown;Unknown;No;HD;20
Unknown;Unknown;No;HD;20
Unknown;Unknown;No;HD;22
Unknown;Unknown;No;HD;19
Unknown;Unknown;No;HD;19
Unknown;Unknown;No;HD;20
Unknown;Unknown;No;HD;19
Unknown;Unknown;No;HD;21
Unknown;Unknown;No;HD;20
Unknown;Unknown;No;HD;20
Unknown;Japan;No;HD;20
Unknown;Unknown;No;HD;21
Imation;Unknown;No;HD;17
Imation;Unknown;Yes;HD;17
Imation;Unknown;Yes;HD;17
Imation;Unknown;Yes;HD;18
Imation;Unknown;Yes;HD;17
Imation;U.S.A.;No;HD;16
Imation;U.S.A.;No;HD;16
Imation;U.S.A.;No;HD;16
Imation;U.S.A.;Yes;HD;18
Imation;U.S.A.;Yes;HD;17
Imation;U.S.A.;Yes;HD;17
Imation;U.S.A.;Yes;HD;16
Imation;U.S.A.;Yes;HD;16
Imation;Unknown;No;HD;16
Imation;Unknown;No;HD;16
Imation;U.S.A.;Yes;HD;17
Imation;U.S.A.;No;HD;16
Imation;U.S.A.;Yes;HD;18
Imation;U.S.A.;No;HD;18
Imation;U.S.A.;Yes;HD;17
Imation;Unknown;Yes;HD;18
Imation;Unknown;No;HD;16
Imation;Unknown;Yes;HD;16
3M;Unknown;Yes;HD;20
3M;Unknown;Yes;HD;21
3M;Unknown;Yes;HD;20
3M;Unknown;Yes;HD;21
3M;Unknown;Yes;HD;20
3M;Unknown;Yes;HD;20
3M;Unknown;Yes;HD;21
3M;Unknown;Yes;HD;20
3M;Unknown;Yes;HD;21
3M;Unknown;Yes;HD;21
3M;Unknown;Yes;HD;20
3M;Unknown;Yes;HD;21
3M;Unknown;Yes;HD;21
3M;Unknown;Yes;HD;20
3M;Unknown;Yes;HD;19
3M;Unknown;Yes;HD;17
3M;Unknown;Yes;HD;19
Imation;U.S.A.;No;HD;16
Imation;U.S.A.;Yes;HD;17
Imation;U.S.A.;Yes;HD;17
Imation;U.S.A.;Yes;HD;18
Imation;U.S.A.;Yes;HD;17
Imation;Unknown;No;HD;18
Imation;Unknown;No;HD;18
Imation;Unknown;No;HD;18
Imation;Unknown;No;HD;18
Imation;Unknown;No;HD;17
Sony;Unknown;No;HD;17
Sony;Unknown;No;HD;17
Sony;Unknown;No;HD;18
Sony;Unknown;No;HD;18
Sony;Unknown;Yes;HD;18
Sony;Unknown;Yes;HD;18
Sony;Unknown;Yes;HD;18
Sony;Unknown;Yes;HD;19
Sony;Unknown;Yes;HD;18
Sony;Unknown;Yes;HD;18
Sony;Unknown;Yes;HD;18
Sony;Unknown;Yes;HD;18
Sony;Unknown;Yes;HD;19
Sony;Unknown;Yes;HD;19
Sony;Unknown;Yes;HD;19
Sony;Unknown;Yes;HD;20
Sony;Unknown;Yes;HD;19
Sony;Unknown;Yes;HD;19
Sony;Unknown;Yes;HD;19
Sony;Unknown;Yes;HD;19
Sony;Unknown;Yes;HD;19
Sony;Unknown;Yes;HD;19
Sony;Unknown;Yes;HD;19
Sony;Unknown;Yes;HD;19
Sony;Unknown;Yes;HD;19
Sony;Unknown;Yes;HD;23
Sony;Unknown;Yes;HD;18
Sony;Unknown;Yes;HD;19
Sony;Unknown;Yes;HD;18
TDK;Unknown;No;HD;20
TDK;Unknown;No;HD;21
TDK;Unknown;No;HD;21
TDK;Unknown;Yes;HD;22
TDK;U.S.A.;Yes;HD;22
TDK;U.S.A.;Yes;HD;21
TDK;U.S.A.;Yes;HD;22
TDK;U.S.A.;Yes;HD;22
TDK;U.S.A.;Yes;HD;21
TDK;U.S.A.;Yes;HD;21
TDK;U.S.A.;Yes;HD;22
TDK;U.S.A.;Yes;HD;22
TDK;Unknown;No;HD;16
TDK;Unknown;Yes;HD;15
TDK;Unknown;Yes;HD;16
TDK;Unknown;Yes;HD;16
TDK;Unknown;Yes;HD;15
TDK;Unknown;Yes;HD;16
TDK;Unknown;Yes;HD;15
TDK;Unknown;Yes;HD;16
TDK;Unknown;Yes;HD;15
TDK;Unknown;Yes;HD;17
TDK;Unknown;Yes;HD;16
TDK;Unknown;Yes;HD;16
TDK;Unknown;Yes;HD;16
TDK;Unknown;Yes;HD;16
Dixons;E.C.;No;HD;17
Dixons;E.C.;No;HD;17
Dixons;E.C.;No;HD;16
Dixons;E.C.;No;HD;16
Dixons;E.C.;No;HD;16
Dixons;E.C.;No;HD;16
Dixons;E.C.;No;HD;16
Dixons;E.C.;No;HD;16
Dixons;E.C.;No;HD;16
Dixons;E.C.;No;HD;16
Dixons;E.C.;No;HD;16
Dixons;E.C.;No;HD;16
Dixons;E.C.;No;HD;16
Unknown;Unknown;Yes;HD;16
Dixons;E.C.;Yes;HD;17
Dixons;E.C.;Yes;HD;17
Dixons;E.C.;Yes;HD;17
Dixons;E.C.;Yes;HD;17
Dixons;E.C.;Yes;HD;18
Dixons;E.C.;Yes;HD;17
Dixons;E.C.;Yes;HD;16
Dixons;E.C.;Yes;HD;17
Dixons;E.C.;Yes;HD;16
Dixons;E.C.;Yes;HD;16
Dixons;E.C.;Yes;HD;16
Dixons;E.C.;Yes;HD;17
Dixons;E.C.;Yes;HD;16
Dixons;E.C.;Yes;HD;16
Dixons;E.C.;Yes;HD;16
Dixons;E.C.;Yes;HD;16
Dixons;E.C.;Yes;HD;17
Dixons;E.C.;Yes;HD;16
Dixons;E.C.;Yes;HD;17
Dixons;E.C.;Yes;HD;16
Dixons;E.C.;Yes;HD;16
Dixons;E.C.;Yes;HD;17
MCN;Japan;Yes;HD;21
MCN;Japan;Yes;HD;21
MCN;Japan;Yes;HD;21
MCN;Japan;Yes;HD;21
MCN;Japan;Yes;HD;21
TDK;E.C.;Yes;HD;16
TDK;E.C.;Yes;HD;16
TDK;Unknown;Yes;HD;17
TDK;Unknown;Yes;HD;18
TDK;Unknown;Yes;HD;18
TDK;Unknown;Yes;HD;17
TDK;Unknown;Yes;HD;18
TDK;Unknown;Yes;HD;17
TDK;Unknown;Yes;HD;18
TDK;Unknown;Yes;HD;17
TDK;Unknown;Yes;HD;18
TDK;E.C.;No;HD;17
TDK;E.C.;No;HD;17
TDK;E.C.;No;HD;17
TDK;E.C.;No;HD;16
TDK;E.C.;No;HD;15
TDK;E.C.;No;HD;16
TDK;E.C.;No;HD;16
TDK;E.C.;No;HD;15
TDK;E.C.;No;HD;15
TDK;E.C.;No;HD;16
TDK;E.C.;No;HD;16
TDK;E.C.;No;HD;16
TDK;E.C.;No;HD;16
TDK;E.C.;No;HD;16
TDK;E.C.;No;HD;16
TDK;E.C.;No;HD;16
TDK;E.C.;No;HD;16
Maxell;England;Yes;HD;15
Unknown;Unknown;Yes;HD;16
Unknown;Unknown;Yes;HD;20
BASF;Unknown;Yes;HD;16
IBM;Japan;Yes;HD;20
Mitsubishi;Japan;Yes;HD;21
Mitsubishi;Japan;Yes;HD;20
Mitsubishi;Japan;Yes;HD;21
Unknown;Japan;Yes;HD;21
Fujifilm;Germany;Yes;HD;17
Fujifilm;Germany;Yes;HD;16
Fujifilm;Germany;Yes;HD;17
Fujifilm;Germany;Yes;HD;17
Fujifilm;Germany;Yes;HD;17
Fujifilm;Germany;Yes;HD;17
Unknown;Unknown;No;HD;19
Unknown;Unknown;No;HD;19
Unknown;Unknown;No;HD;20
Unknown;Unknown;No;HD;16
Unknown;E.C.;No;HD;17
Unknown;E.C.;No;HD;16
Unknown;E.C.;No;HD;16
Unknown;E.C.;No;HD;16
Unknown;E.C.;No;HD;17
Unknown;England;Yes;HD;18
Unknown;Germany;Yes;HD;16
Unknown;Germany;Yes;HD;16
Unknown;E.C.;Yes;HD;17
Unknown;E.C.;Yes;HD;17
Unknown;E.C.;Yes;HD;17
Unknown;Unknown;Yes;HD;16
Unknown;Unknown;Yes;HD;16
Unknown;Unknown;Yes;HD;17
Unknown;Unknown;Yes;HD;17
Unknown;Unknown;Yes;HD;16
Unknown;Unknown;Yes;HD;18
Unknown;Unknown;Yes;HD;18
Unknown;Unknown;Yes;HD;17
Unknown;Unknown;Yes;HD;20
Unknown;Unknown;Yes;HD;17
Unknown;Unknown;Yes;HD;21
3M;Unknown;Yes;HD;17
3M;Unknown;No;HD;17
BASF;Unknown;No;HD;17
BASF;Unknown;No;HD;17
BASF;Unknown;No;HD;16
BASF;Unknown;Yes;HD;17
BASF;Unknown;Yes;HD;16
BASF;Unknown;Yes;HD;16
BASF;Unknown;Yes;HD;17
HEMA;Unknown;Yes;HD;18
HEMA;Unknown;Yes;HD;16
HEMA;Unknown;Yes;HD;16
HEMA;Unknown;Yes;HD;18
HEMA;Unknown;No;HD;16
HEMA;Unknown;No;HD;16
HEMA;Unknown;No;HD;17
Verbatim;Unknown;Yes;HD;18
Verbatim;Unknown;Yes;HD;18
Verbatim;Unknown;Yes;HD;18
Verbatim;Unknown;Yes;HD;18
Verbatim;Unknown;Yes;HD;18
Verbatim;Unknown;Yes;HD;18
Verbatim;Unknown;Yes;HD;19
Fujifilm;Germany;Yes;HD;16
Fujifilm;Germany;No;HD;15
Fujifilm;Germany;No;HD;16
Fujifilm;Germany;No;HD;15
Fujifilm;Germany;No;HD;16
Fujifilm;Germany;No;HD;15
Fujifilm;Germany;No;HD;16
Fujifilm;Germany;No;HD;16
Fujifilm;Germany;No;HD;15
Imation;Unknown;No;HD;16
Imation;Unknown;No;HD;17
Imation;Unknown;No;HD;16
Imation;Unknown;No;HD;15
Imation;Unknown;No;HD;16
Imation;Unknown;No;HD;15
Imation;Unknown;No;HD;16
Imation;Unknown;No;HD;16
Imation;Unknown;No;HD;16
Sony;Unknown;No;HD;17
Sony;Unknown;No;HD;16
Sony;Unknown;No;HD;16
Sony;Unknown;No;HD;16
Sony;Unknown;No;HD;17
Sony;Unknown;No;HD;17
Sony;Unknown;No;HD;16
Sony;Unknown;No;HD;16
Sony;Unknown;Yes;HD;18
Sony;Unknown;Yes;HD;18
Sony;Unknown;Yes;HD;16
Sony;Unknown;Yes;HD;17
Sony;Unknown;Yes;HD;17
Sony;Unknown;Yes;HD;18
Sony;Unknown;Yes;HD;17
Sony;Unknown;Yes;HD;17
Sony;Unknown;Yes;HD;17
Sony;Unknown;Yes;HD;17
Sony;Unknown;Yes;HD;17
Sony;Unknown;Yes;HD;18
Sony;Unknown;Yes;HD;16
Sony;Unknown;Yes;HD;16
Sony;Unknown;Yes;HD;17
Sony;Unknown;Yes;HD;16
Sony;Unknown;Yes;HD;17
Sony;Unknown;Yes;HD;16
Sony;Unknown;Yes;HD;17
Unknown;E.C.;No;HD;18
Unknown;E.C.;No;HD;18
Unknown;E.C.;No;HD;18
Unknown;E.C.;No;HD;18
Unknown;E.C.;No;HD;18
Unknown;Unknown;No;HD;16
Unknown;Germany;Yes;HD;16
Unknown;Germany;Yes;HD;16
Unknown;Germany;Yes;HD;16
Unknown;Germany;Yes;HD;16
Unknown;Germany;Yes;HD;15
Unknown;E.C.;Yes;HD;16
Unknown;E.C.;Yes;HD;16
Unknown;E.C.;Yes;HD;16
Unknown;E.C.;Yes;HD;16
Unknown;E.C.;Yes;HD;16
Unknown;E.C.;Yes;HD;17
Unknown;E.C.;Yes;HD;16
Unknown;E.C.;Yes;HD;16
Unknown;E.C.;Yes;HD;17
Unknown;E.C.;Yes;HD;15
Unknown;E.C.;Yes;HD;15
Unknown;E.C.;Yes;HD;15
Unknown;E.C.;Yes;HD;16
Unknown;E.C.;Yes;HD;16
Unknown;E.C.;Yes;HD;16
Unknown;Unknown;Yes;HD;18
Unknown;Unknown;Yes;HD;16
Unknown;Unknown;Yes;HD;16
Unknown;Unknown;Yes;HD;19
Unknown;Unknown;Yes;HD;20
Unknown;Unknown;Yes;HD;20
Unknown;Unknown;Yes;HD;20
Unknown;Unknown;Yes;HD;20
Unknown;Unknown;Yes;HD;16
Unknown;Unknown;Yes;HD;17
Unknown;Unknown;Yes;HD;19
Unknown;Unknown;Yes;HD;19
Unknown;Unknown;Yes;HD;18
Unknown;Unknown;Yes;HD;17

Of the measured set 64% contained a printed label and 36% did not. 91% of the set was of the type HD and 9% of the type DD. As requested the standard deviation is 2.1.

Weight distribution per part

I've measured the weight of a few independent parts of floppy disks too. Those measurements included 5 metal hubs, 8 aluminium shutters and 4 plastic housings incl. the paper ring. The magnetic disk and spring (out of experience) weigh almost nothing.*

11% Metal hub                    5x total 11g    per piece  2.20g
14% Aluminium shutter            8x total 22g    per piece  2.75g
75% Housing incl. paper ring     4x total 60g    per piece 15.00g
Totals                                    93g    per piece 19.95g

Independent floppy parts

Roughly 75% of the weight consist of the plastic housing and paper ring, 14% shutter and 11% hub. As mentioned other parts (spring, magnetic disk, write protect tab, label) were not measured but are probably negligible.

Method used

I measured the weight of 431 floppy disks (3.5-inch) from several brands such as 3M, BASF, Dixons, Fujifilm, HEMA, IBM, Imation, INMAC, Maxell, MCN, Mitsubishi, Nashua, Sony, TDK, Verbatim and types (DD/HD) using below shown kitchen scale and set to 0 before measuring per floppy.

Electronic digital kitchen scale CM-103/10672Z

Standardization

Regarding the standardization: I could not find any information that indicates there has been a standardized weight for 3.5-inch floppy disks.

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16
  • 12
    Also it wouldn't have made too much sense to standardize the weight as an additional limit. These standards are (mostly) about cross-compatibility, and a couple grams more or less (or even double the weight) would hardly hurt the readers
    – Hobbamok
    Jun 16, 2021 at 12:01
  • 11
    A customer might expect a "double density" disk of the same size to be twice as heavy.
    – JDługosz
    Jun 16, 2021 at 20:55
  • 5
    @JDługosz even more with compressed files are stored :)
    – Raffzahn
    Jan 1, 2022 at 19:59
  • 3
    1.61 µg/bit (I expected them to be heavier) ;)
    – tofro
    Jan 1, 2022 at 22:47
  • 2
    @Zac67 I tend to be pretty precise when I'm not joking;)
    – tofro
    Jan 2, 2022 at 17:49
2

I can't add much to Bob Ortiz's answer, but a small sample of 5 each HD floppies (unlabelled) from three different brands measured on a jeweller's scale resulted in:

Mean              17.2
Median            17.4
Min               16.0
Max               17.6

The measured data are as follows:

Brand               ProductionCountry   LabelPasted HD/DD     Grams
Memorex             China               No          HD        17.6
Memorex             China               No          HD        17.4
Memorex             China               No          HD        17.6
Memorex             China               No          HD        17.6
Memorex             China               No          HD        17.6
Fujifilm (red)      Malaysia            No          HD        16.0
Fujifilm (orange)   Malaysia            No          HD        16.2
Fujifilm (yellow)   Malaysia            No          HD        16.7
Fujifilm (green)    Malaysia            No          HD        17.0
Fujifilm (blue)     Malaysia            No          HD        16.5
“Scottish HE”       Unknown             No          HD        17.6
“Scottish HE”       Unknown             No          HD        17.5
“Scottish HE”       Unknown             No          HD        17.4
“Scottish HE”       Unknown             No          HD        17.2
“Scottish HE”       Unknown             No          HD        17.4

All the disks are NOS, unused, and likely from the same batch from each manufacturer.

Notes:

  1. The Fujifilm disks are different colours. It's clear that the pigment/filler used to mould the different coloured cases affects the mass of the disk. Other disks of the same colour from the same box were within 0.1 g of the measured one.

  2. The oddly-named "Scottish HE" (HE = Higher Education) brand was sold in various universities and colleges in Scotland. There's no indication of the manufacturer, and packaging was generic.

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