The question of how much Steve can carry or lift has been raised several times in the forums, in blog posts, and it was even the topic of a Youtube video featuring SethBling:

Allow me to reiterate the thoughts and arguments brought forward on Steve’s carrying capacity so far. The standard inventory has 4 lines with 9 slots each (one of which is the quick access bar), equaling a total number of 36 item slots. In addition to that, there are also the four armor slots to consider.

Now in vanilla Minecraft the material with the highest density is gold, with a density of 19,300 kg / m³ according to Wikipedia. As Notch mentioned in a blog post in March 2010, a block in Minecraft is a perfect cube of exactly one meter length at every axis, hence a Minecraft gold block weighs exactly 19,300 kg (we are assuming that Minecraft gold is gold in its purest form).

Maximum number of available item slots:

Maximum number of items that can be carried in full stacks:

Maximum number of gold that can be carried:

Let’s not forget about the armor slots, though. Since you need nine gold ingots to craft a gold block, the weight of an ingot is as follows:

For a full armor set, we need a total of 24 ingots:

This brings Steve’s carrying capacity in vanilla Minecraft to a total of 44,518,666.[6]kg … right?

Nope, because we forgot about the 4 x 4 crafting grid at the top of the inventory. So if we throw four stacks of gold blocks to the floor and then place four stacks in the crafting grid, we will be holding four additional stacks of gold in the inventory. Hence ..

Adding that to the amount we calculated earlier, we get ..

.. a total of about 49,459 tons. To put that in comparison: That’s about the total weight of a fleet of 23,462 Tesla Model S cars (without drivers, and assuming that one car weights 2,108 kg), or a bit more than half the weight of the Washington Monument, which weights 82,422 tons according to Wikipedia. So at least as far as weight is concerned, Steve can carry about half of the Washington Monument around in his pockets.

Now that should be the maximum amount of weight Steve can carry, right?

Nope, because there is another stackable item with an even higher density: the Enchanted Golden Apple. Because it is crafted with eight gold blocks, it contains a total gold amount of 154,400 kg per apple. If the whole inventory and the crafting grid are being used, a player can carry a total of 2,560 items.

So if a player were to carry 2,560 Enchanted Golden Apples as well as a full Gold Armor Set, he would carry a total weight of 395,315 tons. That’s more than the estimated weight of the Empire State Building in New York, and more than four and half times the weight of the Washington Monument.

Holy mother of god.