Dungeon Doors

Here is todays puzzle. If you think that you know the answer, please post it in the comments section.

Guido has been thrown into a dungeon. There are 3 doors in the dungeon. The first one is 4 feet wide, 3 feet long, 3 inches thick and has a density of 8746 kg/cubic meter. The second door is 41 inches wide, 41 inches long, 3 inches thick and has a density of 8800 kg/cubic meter. The third door is 5 feet wide, 5 feet long, 1.5 inches thick and has a density of 8470 kg/cubic meter. All three doors have passages behind them. The passage behind the heaviest door leads to freedom. The other two lead to a hungry dragon. Guido does not want to become the dragons lunch. Which door should he choose.

The answer will be posted on monday.