function getSSsize(){
var sheets = SpreadsheetApp.getActiveSpreadsheet().getSheets();
var total = 0;
for (var i=0 ; i<sheets.length ; i++){
var dataValues = sheets[i].getDataRange().getValues();
var item = dataValues[0].length*dataValues.length;
Logger.log('%s: %s', sheets[i].getName(), item);
total += item;
}
Logger.log('Total: %s', total);
}