Convert bytes to TB returns incorrect value

Question

Currently I have a function to convert bytes too TB.

I am using the below formula to convert.

const formatBytesToTB = (a, b = 2) => {
  if (a === 0) {
    return "0 TB";
  }
  return (a / 1099511627776).toFixed(b) + " TB";
};
console.log(formatBytesToTB(109213384704));

The above function is working fine for most of the values that it accepts as bytes

I see some error when bytes value is less than 1 TB.

For example when the input is "109213384704” the function returns “0.10 TB”

Expected output should be “0.09”

I have seen few online converters to test what they return, Google returns 0.10 but rest of the converters show 0.09

Is the function doing right thing ?

Technically, it should be 0.099 if I'm not wrong. What about using .toPrecision instead of .toFixed? — briosheje
– briosheje, Commented Jul 4, 2019 at 7:13
Increase b to be bigger, like 10 and see then. Seems like rounding problem — Justinas
– Justinas, Commented Jul 4, 2019 at 7:13
toFixed is doing the right thing, since the number is 0.099 but you wanted only the first 2 digits so 0.099 is rounded up to 0.10 to account for the x.xx9 that it couldn't display - if you want truncation rather than rounding, pretty sure that could be done with a little toString+substring trickery, though — hanshenrik
– hanshenrik, Commented Jul 4, 2019 at 7:13
more info about strange behaviour of toFixed can be found here and here — mukesh.kumar
– mukesh.kumar, Commented Jul 4, 2019 at 7:20

yuval.bl · Accepted Answer · 2019-07-04 07:21:34Z

1

It seems like a matter of display - Rounding vs Ignoring the decimal after precision value.

The value of 109213384704 / 1099511627776 is 0.099328995

So if you would like to simply ignore whatever comes after the second decimal point, you'll get 0.09.

However,toFixed will round the number to the precision value, so 0.099 will result 0.10 while 0.091 will result with 0.09.

answered Jul 4, 2019 at 7:21

yuval.bl

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2 Comments

user804401 Over a year ago

I want to round off to 2 decimal places but still return accurate result, I dont think toPrecision also works. Is there any other alternative ?

yuval.bl Over a year ago

The current behavior is the more accurate option, as 0.099 is closer to 0.10 then to 0.09. In this regard, it makes no different if you use toPrecision or toFixed

Tushar Gupta · Accepted Answer · 2019-07-04 07:43:46Z

1

109213384704 is 0.099 In Tebibyte(TiB) and 0.10 Terrabyte (TB).

From definitions:

How large is a tebibyte? A tebibyte is larger than the following binary data capacity measures:

A byte -- a TiB is equal to 1,099,511,627,776 bytes.
A kibibyte (KiB) -- a TiB is equal to 1,073,741,824 KiB.
A mebibyte (MiB) – a TiB is equal to 1,048,576 MiB.
A gibibyte -- a TiB is equal to 1,024 GiB.

edited Jul 4, 2019 at 7:43

answered Jul 4, 2019 at 7:19

Tushar Gupta

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