Format file size in Dart

Question

How to format a file size in Dart?

Input: 1000000

Expected output: 1 MB

The input could be either an int or a double for ease of use, and the result should be a String with only one decimal.

score 7 · Answer 1 · answered May 12 '22 at 16:25

7

I made an extension method for this:

extension FileFormatter on num {
  String readableFileSize({bool base1024 = true}) {
    final base = base1024 ? 1024 : 1000;
    if (this <= 0) return "0";
    final units = ["B", "kB", "MB", "GB", "TB"];
    int digitGroups = (log(this) / log(base)).round();
    return NumberFormat("#,##0.#").format(this / pow(base, digitGroups)) +
        " " +
        units[digitGroups];
  }
}

You will need to use the intl package for the NumberFormat class.

You can display bits or bytes using the boolean base64.

Usage:

int myInt = 12345678;
double myDouble = 2546;
print('myInt: ${myInt.readableFileSize(base1024: false)}');
print('myDouble: ${myDouble.readableFileSize()}');

Output:

myInt: 12.3 MB
myDouble: 2.5 kB

Inspired by this SO answer.

answered May 12 '22 at 16:25

leb1755

1,386
2
14
29

This answer, though it works, it is not precise, I had a file with 65mb and your function returned "0.1 GB", which, in my case will is not useful, so I copied [this function](https://github.com/erdbeerschnitzel/filesize.dart/blob/4f7c54dc06647b8368078f6febb83149494698c1/lib/filesize.dart) from this library https://pub.dev/packages/filesize, this is not the best implementation I have ever seen but it fill my use-case and is more precise than your function. – Alex Rintt Nov 09 '22 at 15:41
Comparing this solution with the SO answer referenced, two key points were missed. 1) dart:math's log fn is the natural log, NOT log base 10. Because there isn't a log10 fn in the math library, here is how you'd implement it `double log10(final num x) => log(x) / ln10;`. 2) rounding will not be precise enough, instead using `.floor()` will give the desired result. – Noah Anderson Jan 31 '23 at 20:38

score 1 · Answer 2 · answered Aug 14 '23 at 21:07

Since none of the above were satisfactory for me, I converted this function to a simpler to read, more flexible version:

extension FileSizeExtensions on num {
  /// method returns a human readable string representing a file size
  /// size can be passed as number or as string
  /// the optional parameter 'round' specifies the number of numbers after comma/point (default is 2)
  /// the optional boolean parameter 'useBase1024' specifies if we should count in 1024's (true) or 1000's (false). e.g. 1KB = 1024B (default is true)
  String toHumanReadableFileSize({int round = 2, bool useBase1024 = true}) {
    const List<String> affixes = ['B', 'KB', 'MB', 'GB', 'TB', 'PB'];

    num divider = useBase1024 ? 1024 : 1000;

    num size = this;
    num runningDivider = divider;
    num runningPreviousDivider = 0;
    int affix = 0;

    while (size >= runningDivider && affix < affixes.length - 1) {
      runningPreviousDivider = runningDivider;
      runningDivider *= divider;
      affix++;
    }

    String result = (runningPreviousDivider == 0 ? size : size / runningPreviousDivider).toStringAsFixed(round);

    //Check if the result ends with .00000 (depending on how many decimals) and remove it if found.
    if (result.endsWith("0" * round)) result = result.substring(0, result.length - round - 1);

    return "$result ${affixes[affix]}";
  }
}

Sample output:

1024 = 1 KB  
800 = 800 B  
8126 = 7.94 KB  
10247428 = 9.77 MB

Format file size in Dart

2 Answers2