How much does the Doctor's TARDIS weigh from the outside?

Lady Romana is quoted as saying a TARDIS weights 5x10^6 kilograms, but I've also read that she was mistaken in this or that she was referring to the inside.

The Doctor's TARDIS has been moved a number of times and has landed on soft ground and not sunk in at all. This indicates the full weight of the interior is not felt from the exterior. But in The Parting of the Ways, Rose, Jackie, and Mickey use a large truck with chains to free up part of the interior of the TARDIS, and when they pull with the truck, the TARDIS doesn't just get pulled along on the ground, so, at least when the door is open, there's some connection between the weight inside and the outside shell.

I've searched for this and Romana's answer is the only one I find, but if that were true and it weight that much on the outside, people could not pick it up and move it.

How much does the Doctor's TARDIS weight from the outside?

Answer

I've never seen a in-universe explanation (Possibly because that's something they have avoided defining, lest it cause complications later), but observing it's behavior, I'd guess the following:

The external shell has a weight consistent with what the chameleon circuit has modeled it upon. For example, the Doctor's Tardis is set up as a police box, and, being made primarily of wood, isn't that heavy. Other disguised Tardis examples, however, weren't so light -- The Master's Tardis, disguised as the Melkur, should have weighed about the same as a stone statue of it's size. That being said, I've never seen anything to really confirm this, it's just supposition.

As to when Mickey, Rose and Jackie were pulling on the console, the cable they connected was crossing the threshold into the main Tardis; they were pulling against the actual full weight of the Tardis, not just it's exterior shell. (Goes back to the whole Dimensionally transcendental thing; just as the exterior shape doesn't pass back physical requirements to the interior shape, so does force exerted on the inside not translate to force on the outside) Had they simply hooked the cable around the Tardis, it most likely would have moved quite easily. One way to think of it is that the door of the Tardis is an opening to a Pocket Universe; it doesn't CONTAIN it, so much as provide a portal to it.