https://stackoverflow.com/questions/9190190/how-to-use-curl-to-compare-the-size-of-the-page-with-deflate-enabled-and-without

compare.sh

#!/usr/bin/env bash
set -e

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

compare() {
  echo "URI: ${1}"

  SIZE=$(curl -so /dev/null "${1}" -w '%{size_download}')
  SIZE_HUMAN=$(bytesToHuman "$SIZE")
  echo "Uncompressed size : $SIZE_HUMAN"

  SIZE=$(curl --compressed -so /dev/null "${1}" -w '%{size_download}')
  SIZE_HUMAN=$(bytesToHuman "$SIZE")
  echo "Compressed size   : $SIZE_HUMAN"
}

compare https://stackoverflow.com/q/9190190/1480391