function findSize() {
    var fileInput =  document.getElementById("fUpload");
    try{
        alert(fileInput.files[0].size); // bytes del file
    }
    try{
        alert(fileInput.files[0].fileSize); //bytes del file con firefox
    }
    catch(e){
        var objFSO = new ActiveXObject("Scripting.FileSystemObject");
        var e = objFSO.getFile( fileInput.value);
        var fileSize = e.size;
        alert(fileSize);    // Bytes del file con Internet Explorer
    }
}