created_at2018-08-11 20:31:46.412064
updated_at2024-04-27 16:13:00.688332
descriptionA crate for expressing, formatting, and interacting with file sizes
Mahmoud Al-Qudsi (mqudsi)



PrettySize, rust edition

A comprehensive file size crate for rust applications, meant to be light and effective. Includes utilities for human-readable formatting of file sizes as well as converting between different base-two and base-ten size units and performing both mathematical and logical operations on strongly-typed file sizes.

See the crate documentation for a more complete summary of what this crate can do and how to use it.


PrettySize provides

  • a Size type that can be used to hold a strongly-typed size (e.g. let size = Size::from_gigabytes(4)) and perform operations on it,
  • definitions for the base-two and base-ten file size units defined as pub const in the size::consts namespace, available both in abbreviated and unabridged forms (i.e. consts::KiB and consts::KIBIBYTE or consts::GB and consts::GIGABYTE),
  • an std::Display impl for Size to automatically display sizes in a human-readable format, automatically choosing the best size unit and numeric precision to give the nicest results (you can also use Size::to_string() instead).
  • a Size.format() method that gives you more control over how sizes are converted to a textual representation, letting you to specify the base of the human-readable units and their style (smart, abbreviated, or full; plus their lowercase variants).
  • mathematical and logical operations on strongly-typed Size values,
  • full support for expressing negative sizes (e.g. the difference between two sizes, or the amount of space reclaimed on a disk)
  • serialization to/from bare byte fields in network payloads or other api requests/responses
  • parsing sizes from text representation in a wide variety of formats

This crate can also be used in no_std mode (by compiling with default features disabled). This disables string conversion/formatting/parsing but keeps all the strongly-typed size conversion and mathematical/logical operations available.

This crate is free of any dependencies.



size = "0.5.0-preview2"

and in your code:

use size::{Base, Size};
// You can use/import consts representing base2/base10 sizes individually
// as (e.g.) size::KiB, or import all with `use size::consts::*`

fn main() {
  // Create strongly-typed sizes:
  let byte_count = Size::from_kilobytes(42);
  assert_eq!(42_000, byte_count.bytes());

  // Use predefined constants for the various units
  let byte_count = 42 * size::KiB;
  assert_eq!(43_008, byte_count);

  // `Size` can take any numeric type you throw at it
  let byte_count = Size::from_mib(0.040055);
  assert_eq!(byte_count.bytes(), 42_000);

  // And for those of you that haven't yet drunk the base-two Kool-Aid:
  let file_size = Size::from_kb(42);
  assert_eq!(file_size.bytes(), 42_000);

  println!("{}, I say!", file_size);
  // prints "41 KiB, I say!"

  // Override the default choice of base-2 units
  println!("{}, I meant!", file_size.format().with_base(Base::Base10));
  // prints "42 KB, I meant!"

  // Add and subtract strongly-typed sizes, even with different underlying types
  let sum = Size::from_mb(1.0) + Size::from_kb(200);
  assert_eq!(sum.bytes(), 1_200_000);

  // Multiply and divide strongly-typed sizes by scalar values
  let new_size = Size::from_mib(2) * 2;
  assert_eq!(new_size, Size::from_mib(4));

  // Compare sizes for equality or order
  let size1 = Size::from_gigabytes(2);
  let size2 = Size::from_gibibytes(1.99);
  assert!(size1 < size2);

  // Parse sizes from textual representations
  let size1 = Size::from_str("12 KiB").unwrap();
  let size2 = Size::from_str("42mb").unwrap();

Parsing and formatting

The size crate supports parsing textual representations of file sizes into strongly typed Size objects, both via the Size::from_str() function and its FromStr implementation that lets you call "1234 kilobytes".parse().

The Size type implements std::fmt::Display (in addition to many other traits), which provides a facility to generate properly formatted textual representations of file sizes via the Size::to_string() impl of the ToString trait or when used in a format!(..., Size) context.

By default, Size objects are formatted as base-2 (KiB, MiB, etc) with heuristically chosen precision and units. The member function Size::format() can be used to override the unit base (e.g. MB vs MiB) and whether or not abbreviated unit names are used (e.g. KiB vs Kebibyte).

Feel free to open a GitHub issue or PR if you need further control over formatting (precision, case, etc)!

no_std usage

Add the crate to Cargo.toml with default-features disabled for no_std support:

size = { version = ..., default-features = false }

Building in no_std mode disables support for floating point Size operations/conversions as well as string formatting and conversion.

serde support

For serialization and deserialization support, add the size crate to your Cargo.toml with the serde feature enabled:

size = { version = ..., features = [ "serde" ] }

The Size type is serialized/deserialized transparently. This means that it acts as if it were a u64 field denoting the size in bytes. This was done to allow directly deserializing from network payloads from languages/apis that do not express sizes as strongly typed fields (and vice-versa).

As a concrete example, let's pretend you have the following struct that contains a Size field:

#[derive(Serialize, Deserialize)]
struct File {
    path: PathBuf,
    size: Size,

Using JSON as an example, the File type above will serialize to/from the following:

    "path:" "/foo/bar",
    "size:" 1024

As you can see, the size field has been serialized directly to a numeric value (and not a Size object containing that number value).

Parsing sizes from strings

The FromStr impl or the static Size::from_str() member function can be used to parse sizes from text, and support a wide variety of input formats and representations:

let size1 = Size::from_str("123456").unwrap();
let size2 = Size::from_str("17mib").unwrap();
let size3 = Size::from_str("12.8 KB").unwrap();
let size4 = Size::from_str("18.9 gigabytes").unwrap();


This project started off as a port of Mahmoud's PrettySize.NET library from C# to Rust. Like the C# edition of this project. Rust's richer enum types and powerful generics made implementing a custom Size generic over the number type without verbosity additionally possible. Its scope has since grown considerably.


PrettySize is written and maintained by Mahmoud Al-Qudsi of NeoSmart Technologies and released to the general public under the terms of the MIT public license.


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cargo fmt