有一个开源项目可以做到这一点，甚至更多。

7.Bits().ToString();         // 7 b
8.Bits().ToString();         // 1 B
(.5).Kilobytes().Humanize();   // 512 B
(1000).Kilobytes().ToString(); // 1000 KB
(1024).Kilobytes().Humanize(); // 1 MB
(.5).Gigabytes().Humanize();   // 512 MB
(1024).Gigabytes().ToString(); // 1 TB

http://humanizr.net/#bytesize

https://github.com/MehdiK/Humanizer

下面是@ deepe1的BigInteger版本的答案，它绕过了long的大小限制(因此支持yottabyte和理论上的任何后面的限制):

public static string ToBytesString(this BigInteger byteCount, string format = "N3")
{
    string[] suf = { "B", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB", "YiB" };
    if (byteCount.IsZero)
    {
        return $"{0.0.ToString(format)} {suf[0]}";
    }

    var abs = BigInteger.Abs(byteCount);
    var place = Convert.ToInt32(Math.Floor(BigInteger.Log(abs, 1024)));
    var pow = Math.Pow(1024, place);

    // since we need to do this with integer math, get the quotient and remainder
    var quotient = BigInteger.DivRem(abs, new BigInteger(pow), out var remainder);
    // convert the remainder to a ratio and add both back together as doubles
    var num = byteCount.Sign * (Math.Floor((double)quotient) + ((double)remainder / pow));

    return $"{num.ToString(format)} {suf[place]}";
}

我喜欢使用以下方法(它支持高达tb，这在大多数情况下已经足够了，但它可以很容易地扩展):

private string GetSizeString(long length)
{
    long B = 0, KB = 1024, MB = KB * 1024, GB = MB * 1024, TB = GB * 1024;
    double size = length;
    string suffix = nameof(B);

    if (length >= TB) {
        size = Math.Round((double)length / TB, 2);
        suffix = nameof(TB);
    }
    else if (length >= GB) {
        size = Math.Round((double)length / GB, 2);
        suffix = nameof(GB);
    }
    else if (length >= MB) {
        size = Math.Round((double)length / MB, 2);
        suffix = nameof(MB);
    }
    else if (length >= KB) {
        size = Math.Round((double)length / KB, 2);
        suffix = nameof(KB);
    }

    return $"{size} {suffix}";
}

请记住，这是为c# 6.0(2015)编写的，因此对于较早的版本可能需要进行一些编辑。

下面是一个自动确定单位的简明答案。

public static string ToBytesCount(this long bytes)
{
    int unit = 1024;
    string unitStr = "B";
    if (bytes < unit)
    {
        return string.Format("{0} {1}", bytes, unitStr);
    }
    int exp = (int)(Math.Log(bytes) / Math.Log(unit));
    return string.Format("{0:##.##} {1}{2}", bytes / Math.Pow(unit, exp), "KMGTPEZY"[exp - 1], unitStr);
}

“b”代表bit，“b”代表Byte，“KMGTPEZY”分别代表kilo, mega, giga, tera, peta, exa, zetta和yotta

可以将ISO/IEC80000纳入考虑范围:

public static string ToBytesCount(this long bytes, bool isISO = true)
{
    int unit = isISO ? 1024 : 1000;
    string unitStr = "B";
    if (bytes < unit)
    {
        return string.Format("{0} {1}", bytes, unitStr);
    }
    int exp = (int)(Math.Log(bytes) / Math.Log(unit));
    return string.Format("{0:##.##} {1}{2}{3}", bytes / Math.Pow(unit, exp), "KMGTPEZY"[exp - 1], isISO ? "i" : "", unitStr);
}

这可能不是最有效或最优化的方法，但如果您不熟悉对数数学，它更容易阅读，并且对于大多数情况来说应该足够快。

string[] sizes = { "B", "KB", "MB", "GB", "TB" };
double len = new FileInfo(filename).Length;
int order = 0;
while (len >= 1024 && order < sizes.Length - 1) {
    order++;
    len = len/1024;
}

// Adjust the format string to your preferences. For example "{0:0.#}{1}" would
// show a single decimal place, and no space.
string result = String.Format("{0:0.##} {1}", len, sizes[order]);

[DllImport ( "Shlwapi.dll", CharSet = CharSet.Auto )]
public static extern long StrFormatByteSize ( 
        long fileSize
        , [MarshalAs ( UnmanagedType.LPTStr )] StringBuilder buffer
        , int bufferSize );


/// <summary>
/// Converts a numeric value into a string that represents the number expressed as a size value in bytes, kilobytes, megabytes, or gigabytes, depending on the size.
/// </summary>
/// <param name="filelength">The numeric value to be converted.</param>
/// <returns>the converted string</returns>
public static string StrFormatByteSize (long filesize) {
     StringBuilder sb = new StringBuilder( 11 );
     StrFormatByteSize( filesize, sb, sb.Capacity );
     return sb.ToString();
}

来自:http://www.pinvoke.net/default.aspx/shlwapi/StrFormatByteSize.html