Blue whales can reach a length of 30 meters. There were Sauropods that exceeded that length, but Blue Whales have a far bigger volume than those dinosaurs. Remember that sauropods only get such lengths because of their long thin necks and tails, while Blue Whales are fat and massive over almost their entire length.
There might have been a Sauropod that had a bigger volume than Blue Whales, it is called Amphicoelias. But since only a few bones of Amphicoelias have been found we can't know for certain how big it was.