Let's start with a real world conversion. A typical block in Minecraft, such as a block of gold, is a 1 meter cube, so its volume is 1 cubic meter, the surface area of any of its sides is 1 square meter, and the length of any of its edges is 1 meter. (Remember, the diameter (distance across traveling through the center) of a sphere is twice the radius (the distance from the center of a sphere to a point on the surface), and "·" is a multiplication symbol. Here's a unit converter.)

In the default (and the largest permitted) world, the distance between the center of the map and the world boundary along the X or Z axis is 30 million blocks (about 4.7 times the Earth's equatorial radius). So, the surface area of a Minecraft world is (30,000,000·2)^2 = 3.6 quadrillion square meters (about 7.1 times the Earth's surface area). This is the answer you'll usually find when you search the question online (apart from the planet being infinite).

But a Minecraft world is a square sheet, and in real life, non-spherical objects at the scale of planets will promptly collapse into spheres due to their gravity. Also, regardless of your coordinates, the gravity in the game is exactly the same as far as you can measure it (which is how gravity on a spherical body works). These facts tell us that the planet is spherical, apart from the surface topography.

The formula for the radius of a sphere from its surface area is (1/2)·square root of (surface area/pi). So, a sphere with a surface area of 3.6 quadrillion square meters has a radius of about 16,925,688 meters, which is about 2.7 times the Earth's radius. However, as I said, Minecraft worlds are square sheets, and most stuff in Minecraft is cubic. Cubes are basically six squares stuck together, so let's treat Minecraft as a cube with each side having a surface area of 3.6 quadrillion square meters. We get a radius of about 41,459,298 meters, which is about six and a half times Earth's radius and about 67% greater than Neptune's equatorial radius. But since surface topography will increase the surface area of an object, and the bottom of the bedrock layer (level 0) has a smooth surface, let's establish this distance as the distance between the center of the planet and level 0 in the Overworld. Since sea level is 63 blocks above the bottom of the bedrock layer (in the default world), the radius of Minecraft is thus about 41,459,361 meters, barely different from the previous value on a planetary scale. With this value and the sphere volume formula (4/3)·pi·(radius^3), we get a volume of about 298.51 sextillion cubic meters, which is about 275 times the Earth's volume and about 5 times Neptune's.

What about Minecraft's mass? Finding that out is a little bit more complicated. First, we need to know Minecraft's surface gravity. It's complicated, because different entities in Minecraft fall at different rates. Exactly why is to be explained another day, but magnetic force could affect the acceleration of an object if there's enough of it. One experiment found that in the Overworld, sand blocks have an acceleration of 16.9 meters per second squared, which is about 72% more than on Earth (see video description; he miscalculated in the video). We'll use that, because sand is usually non-magnetic.

In Newtonian physics, the force acting on an object is equal to the mass of the object multiplied by the acceleration of the object that the force causes. A block of sand has a density of 1.6 grams per cubic centimeter, so it has a mass of 1,600 kilograms (since 1 g/cm^3 = 1000 kg/m^3). Thus, the force acting between the planet and a block of sand at its surface, or the weight of the sand block, is 1,600·16.9 = 27,040 newtons.

The formula for the force between two objects in Newtonian physics is gravitational constant·((mass of the first object·mass of the second object)/(distance between the centers of mass of the objects^2)). So, with the formula and our numbers, we can use algebra to find the mass of Minecraft:

(6.67408·10^-11)·((mass of Minecraft·1,600)/(radius of Minecraft^2)) = 27,040

mass of Minecraft = about 435.25 septillion kilograms

That's about 73 times more massive than Earth and about 77 percent of Saturn's mass.

Dividing the mass by the volume, we find that Minecraft has an average density of about 1,458 kilograms per cubic meter (1.458 grams per cubic centimeter), which is in the range of a gaseous planet like Jupiter, not a terrestrial planet like Earth (and is a little bit more than the average density of the Sun in real life). This suggests that the planet, like ours, has a dense core, and that the Void is filled with gas. Minecraft is a giant planet with a solid surface, and in real life, such planets are rare, because they usually suck up gas!

And that settles one of the oldest questions in the game.