Fun fact: The original snippet posted here was the most copied Java snippet of all time on Stack Overflow, and it was flawed. It was fixed, but it got messy.

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Source: Formatting byte size to human readable format | Programming.Guide

SI (1 k = 1,000)

public static String humanReadableByteCountSI(long bytes) {    if (-1000 < bytes && bytes < 1000) {        return bytes + " B";    }    CharacterIterator ci = new StringCharacterIterator("kMGTPE");    while (bytes <= -999_950 || bytes >= 999_950) {        bytes /= 1000;        ci.next();    }    return String.format("%.1f %cB", bytes / 1000.0, ci.current());}

Binary (1 Ki = 1,024)

public static String humanReadableByteCountBin(long bytes) {    long absB = bytes == Long.MIN_VALUE ? Long.MAX_VALUE : Math.abs(bytes);    if (absB < 1024) {        return bytes + " B";    }    long value = absB;    CharacterIterator ci = new StringCharacterIterator("KMGTPE");    for (int i = 40; i >= 0 && absB > 0xfffccccccccccccL >> i; i -= 10) {        value >>= 10;        ci.next();    }    value *= Long.signum(bytes);    return String.format("%.1f %ciB", value / 1024.0, ci.current());}

Example output:

                              SI     BINARY                   0:        0 B        0 B                  27:       27 B       27 B                 999:      999 B      999 B                1000:     1.0 kB     1000 B                1023:     1.0 kB     1023 B                1024:     1.0 kB    1.0 KiB                1728:     1.7 kB    1.7 KiB              110592:   110.6 kB  108.0 KiB             7077888:     7.1 MB    6.8 MiB           452984832:   453.0 MB  432.0 MiB         28991029248:    29.0 GB   27.0 GiB       1855425871872:     1.9 TB    1.7 TiB 9223372036854775807:     9.2 EB    8.0 EiB   (Long.MAX_VALUE)

FileUtils.byteCountToDisplaySize(long size) would work if your project can depend on org.apache.commons.io.

JavaDoc for this method

Use an Android built-in class

For Android, there is a class, Formatter. Just one line of code and you are done.

android.text.format.Formatter.formatShortFileSize(activityContext, bytes);

It is like formatFileSize(), but trying to generate shorter numbers (showing fewer decimals).

android.text.format.Formatter.formatFileSize(activityContext, bytes);

It formats a content size to be in the form of bytes, kilobytes, megabytes, etc.