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Golang helpers for data sizes (kilobytes, petabytes), human readable sizes, parsing
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datasize Build Status

Golang helpers for data sizes


Just like time package provides time.Second, time.Day constants datasize provides:

  • datasize.B 1 byte
  • datasize.KB 1 kilobyte
  • datasize.MB 1 megabyte
  • datasize.GB 1 gigabyte
  • datasize.TB 1 terabyte
  • datasize.PB 1 petabyte
  • datasize.EB 1 exabyte


Just like time package provides duration.Nanoseconds() uint64 , duration.Hours() float64 helpers datasize has

  • ByteSize.Bytes() uint64
  • ByteSize.Kilobytes() float4
  • ByteSize.Megabytes() float64
  • ByteSize.Gigabytes() float64
  • ByteSize.Terabytes() float64
  • ByteSize.Petebytes() float64
  • ByteSize.Exabytes() float64

Warning: see limitations at the end of this document about a possible precission loss

Parsing strings

datasize.ByteSize implements TextUnmarshaler interface and will automatically parse human readable strings into correct values where it is used:

  • "10 MB" -> 10* datasize.MB
  • "10240 g" -> 10 * datasize.TB
  • "2000" -> 2000 * datasize.B
  • "1tB" -> datasize.TB
  • "5 peta" -> 5 * datasize.PB
  • "28 kilobytes" -> 28 * datasize.KB
  • "1 gigabyte" -> 1 * datasize.GB

You can also do it manually:

var v datasize.ByteSize
err := v.UnmarshalText([]byte("100 mb"))


Bytesize.String() uses largest unit allowing an integer value: * (102400 * datasize.MB).String() -> "100GB" * (datasize.MB + datasize.KB).String() -> "1025KB"

Use %d format string to get value in bytes without a unit

JSON and other encoding

Both TextMarshaler and TextUnmarshaler interfaces are implemented - JSON will just work. Other encoders will work provided they use those interfaces.

Human readable

ByteSize.HumanReadable() or ByteSize.HR() returns a string with 1-3 digits, followed by 1 decimal place, a space and unit big enough to get 1-3 digits

* `(102400 * datasize.MB).String()` -> `"100.0 GB"`
* `(datasize.MB + 512 * datasize.KB).String()` -> `"1.5 MB"`


  • The underlying data type for data.ByteSize is uint64, so values outside of 0 to 2^64-1 range will overflow
  • size helper functions (like ByteSize.Kilobytes()) return float64, which can't represent all possible values of uint64 accurately:
    • if the returned value is supposed to have no fraction (ie (10 * datasize.MB).Kilobytes()) accuracy loss happens when value is more than 2^53 larger than unit: .Kilobytes() over 8 petabytes, .Megabytes() over 8 exabytes
    • if the returned value is supposed to have a fraction (ie (datasize.PB + datasize.B).Megabytes()) in addition to the above note accuracy loss may occur in fractional part too - larger integer part leaves fewer bytes to store fractional part, the smaller the remainder vs unit the move bytes are required to store the fractional part
  • Parsing a string with Mb, Tb, etc units will return a syntax error, because capital followed by lower case is commonly used for bits, not bytes
  • Parsing a string with value exceeding 2^64-1 bytes will return 2^64-1 and an out of range error
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