I'm not aware of any canonical references that quote the mass of any starship aloud. If there are any, I'd sure like to know what episodes they're in. Ditto for length figures and other size measurements.
Size is easier to estimate than mass, because we have geometry at our disposal, and objects of known size (i.e. people) to make comparisons.
To estimate mass, we have to be more indirect. Starships don't gravitationally disrupt the planetary systems they pass through, so they can't be too heavy. Additionally, those that land on planet surfaces (e.g., Bounty
) can't be so heavy that they sink into the ground.
For reference, the displacement of the real-world aircraft carrier USS Enterprise
(CVN-65) is on the order of 95,000 tons, nearly one-third of the quoted 300,000 metric tons for the starship. Given what the starship does, I've always thought that therefore that's just too light a figure for the starship's mass. How heavy it could get before it started interfering with the orbits of planetary satellites, I don't know, but I'd imagine it to be as heavy as it could get without being disruptive (when all its power systems are turned off).
I agree that the nacelles are probably the densest parts.
Just my two cents.