The scale of 40K ships is apparently staggering. I know that Imperial Star Destroyers are 1.6 to 1.8 Kilometers and are crewed by/carry 10,000. Not to mention the 6 full fighter squadrons, 5 AT-ATs and a myriad of drop craft or captured enemy vessels. Then you have Executor, Darth Vader's Super Star Destroyer at 8km and aside from the Death Star, the largest starship in that universe. To build the Executor, the Empire had to strip mine an entire planet. So the Imperium is regularly destroying entire worlds for its warships. Intense.

A whole planet's worth of metals to build one ship is nonsense. From the amount of iron in the Earth for example you could create 2 billion Death Stars, which was far larger than the Executor. Source

In 40k even primitive worlds are capable of mining the necessary amount of minerals for cruisers (though it does admittedly take many decades) so Forgeworlds and orbital shipyards should have no problem.

Umm. Your source says we'd have to mine the core. Pretty sure we'd destroy Holy Terra in the process. And even if we didn't mine that deep, I meant that the planet was left uninhabitable. The industry needed to mine that much produces a lot of waste material, polluting both air and water. And it does boil down to cost. It is much cheaper to mine the surface than the core. Of course there are billions of uninhabitable, resource rich worlds in the galaxy. Put a shipyard in orbit, blast the planet apart and mine the asteroids left behind. Oddly enough, that is what the Empire told the scientists who designed the Death Star that it would be used for similar mining purposes.

My point was that it wouldn't take a whole planets resources to create just one ship, rather a world could produce hundreds, thousands or millions before exhausting it's resources.

You wouldn't need to mine your Homeworld, though. Our Solar System alone is chock-a-blok with all the goodies would ever need for a looooooong time. And that's only looking at the Asteroid Belt and the Kuiper Belt. Add in what you could mine from Mercury (that must be one gigantic strip-mine in the far future!) and from any and all of the moons and planets, and you could build Emperor knows how many ships.
Once outside the local System, you have the rest of the galaxy to mine. Who knows what metals can be mined from a gas giant? Who knows what could be done by using Venus as a planet-sized smelter, or using the pressure of the deep layers of something like Jupiter or Saturn?
When it comes to the crew of Astartes ships, wouldn't this be a lot lower because of automation? Loads of Servitors would enable smaller Chapters to crew their fleet; otherwise each Chapter would need a planet's worth of warm bodies just to keep them void-capable.

GFP

In Execution Hour the stated crew of the Macharius is 10,000 give or take a couple of hundred, whith room for a couple of Regiments of Ig plus Vehicles if you wanted to pack the bulkeads and nooks and crannies with stuff.
As to the above post by Warlock, the battleship is off I think. There are references to 5km long battleships. But Irrc the " standard" as much as there is one, is 7-8 km for most battleships, also shows up in Execution Hour and Shadowpoint.
A couple of older novels have 5km Battleships.
In a short story of Into the Maelstrom, (lol, really old book) the Ultramarines battlebarge, which is a converted battleship is 10km long.

On a side note, someone kinda worked out the math for a battleship, based off Execution Hour and Shadowpoint. If the Macharius is 3km long with a crew of 10,000 and a battleship is rouchly 8km long, with the design style and pictures going off of( really really rough estimate), the battleship sould be 3 times as wide, 2.5 times as long, and 3 times as tall. So, 10,000* 3(3 times width)*3(for the height) * 2.5( for the length, equals 225,000 crew roughly. Except that battleships have consequently bigger guns and more of them plus larger engines and reactors requiring a larger ratio of crew per gun and reactor than the Macharius. Also a consequently larger Armsmen crew as they are bigger and more valuable targets.
Another side note, lol. Shadowpoint puts the Cobra destroyer as .5 km irrc with a crew of only 800. Make of that what you will.

Found another one.
Escort = 3 km I think. Lots my place in the book.

I would suggest you get a few of the rouge trader source books.

They have lots of juicy fluff, espescially regarding 40k ships.

Sure most of the 40k ship sizes are retarded, but they are supposed to be retarded.


The general 40k ship sizes go as this.

Transport.
<1 kilometer-ish. That's the small ones, there are super transports in 40k as well though.
Escort.
1-1.5 kilometer. "Small" ships, like the cobra. Designed to flank foes and operate in squads.
Light cruiser.
4-6 Kilometer. A smaller cruiser, not super common.
Cruiser.
7-ish Kilometer. The standard fighting vessel, every imperial fleet has them. And they are the most numerous. (Perhaps some escorts are more common, i might be wrong though)
Heavy cruiser.
7-10 kilometer. A beefed up cruiser, our term for it would probably be pocket battleship.
Looks big and honking. Big guns, but still only is a cruiser.
Battleship.
8-12 Kilometer. The biggest of the lot. Simply put.


The problem with 40k ships, is that their numbers are never written down properly. Hence why there are so many versions.

Rouge trader has a bunch of vessels written down. And should be the best bet you have for 40k ships.

They state width and length, how much crew and how may "slots" you can use.
The game have slots which the players themselves put in things like engines, gellar fields and all other goodies in. It is explained well in the rulebook.

It's fun to sit and build ships as well. Good luck with the hunt.

I'm wondering what the size was of the Vengeful Spirit. At any one time it seems to have a minimum of four companies onboard, although it would seem even more than this, aswell as the Dies Irae, and I imagine a healthy portion of Byzant Janizars.