The heaviest dinosaur known from good skeletons is brachiosauros between 30,000 and 60,000 kilograms (70,000 and 130,000 lb

Edit: Every dinosaur weight or mass you have ever heard is an estimate. Estimates are difficult when you only have the bones because of the uncertainties of unknown soft tissue. Also the largest known dinosaurs arrn't very complete which makes estimating even harder. In short there is no straight answer.

Take Brachiosaurus brancai (some call it Giraffatitan brancai ). It has been estimated as low as 15 tons and as high as 80 tons using different estimates.
Those two estimates are extreme and are generally thought to be wrong. Most estimates these days put it in the 25-30 ton range.

Argentinosaurus is undoubtingly a massive animal but it isn't fully known. There are a lot of uncertainties as to its exact proportions. Estimates have ranged from 60 -100 tons.

There are other, even less complete giant dinosaurs which 'might' be bigger.

Here are some other potential candidates to look into:
Amphicoelias, Futalognkosaurus, Puertasaurus, Paralititan, Antarctosaurus, Sauroposeidon, Turiasaurus