calc-size-kb-files-google-drive.js

[...document.getElementsByClassName("a-t-J a-Wa-ka l-oi-cc l-t-Q a-t-J-yl")]
  .map(element => {
    const sizeTextSplit = element.childNodes[3].childNodes[0].childNodes[1].childNodes[0].innerText.split(
      " "
    );
    return {
      size: Number(sizeTextSplit[0]),
      unit: sizeTextSplit[1],
      node: element
    };
  })
  .map(element => {
    const SIZES_KB = { MB: 1024, GB: 1048576, KB: 1 };
    return {
      size: element.size * SIZES_KB[element.unit],
      unit: element.unit,
      node: element.node
    };
  })
  .reduce((sum, element) => sum + element.size, 0);