Answer by Camilo Martin for A standard tool to convert a byte-count into human KiB MiB etc; like du, ls1

Here's a bash-only option, no bc or any other non-builtins, + decimal format and binary units.

bytesToHuman() {
    b=${1:-0}; d=''; s=0; S=(Bytes {K,M,G,T,P,E,Z,Y}iB)
    while ((b > 1024)); do
        d="$(printf ".%02d" $((b % 1024 * 100 / 1024)))"
        b=$((b / 1024))
        let s++
    done
    echo "$b$d ${S[$s]}"
}

Examples:

$ bytesToHuman 123456789
117.73 MiB

$ bytesToHuman 1000000000000 # "1TB of storage"
931.32 GiB                   #  1TB of storage

$ bytesToHuman 
0 Bytes

Should perform well on any version of Bash out there (including MSYSGit's Bash for Windows).