curl https://example.com/bigcsv.csv --silent  --write-out "%{size_download}\n" --output /dev/null

curl https://example.com/bigcsv.csv -H "Accept-Encoding: gzip,deflate" --silent  --write-out "%{size_download}\n" --output /dev/null

The first command will return smaller number of bytes than the second one.

curl -sSL -D - example.com -o /dev/null