I'll be using US Navy ships for the comparison for a few reasons:

1) I live in the US, so it's easiest for me to find information on them.

2) I'm most familiar with the US Navy so it's easier to make comparisons.

3) The US Navy is the largest on Earth currently(To my knowledge), and is likely the best comparison to the Imperium ships.

So! Let's get to the numbers, shall we?

**Creating Our Fictional 'Modern' Ship**

Let's start with a Carrier, since the information is easiest to find, as they are still in active service. These numbers are based on the Gerald R. Ford-class USN Supercarrier coming into service sometime this year.

**Length**: 1106ft(337m)

**Beam(Width)**: 256ft(78m)

**Height**: 250ft(76m)

**Crew Complement**: 4660(Planned)

Battleship is a little more difficult. The last active service USN Battleship was the Missouri(Iowa-Class), in the first Gulf War. However, larger Battleships were planned, though exact details are impossible as none were completed, and no construction was ever begun. We'll be going with the proposed Montana-class for the comparison, as they were larger than the Iowa and near-exact details are available.

**Length:**921ft 3in(280.80m)

**Beam(Width):**121ft(36.93m) (Fun fact: They would have been the first US Battleships proposed that could not fit through the Panama Canal)

**Height:**Height is difficult to determine, as only Draft(Height below the waterline) is listed, at 36ft(10.97m). However, the Missouri's height is listed at 209ft 8in(63.9m) from keel to mast, and the draft at 38ft(11.6m). Meaning, if the numbers are compared, we can arrive at 199ft(60.65m) for the full height of the Montana-class from keel to mast.

**Crew Complement:**2355(Planned)

Now, to arrive at the size of our fictional ship that could compare to an Imperial Battleship, we have to combine these two numbers. However, we don't want to simply add them, as we don't want to compare two ships to one. Some positions between a Battleship and Carrier are redundant and can be eliminated. We're not attempting to duct tape two ships together, we want to combine them into one 'supership'. So we'll be adding the numbers together, and then subtracting half of the average of the two ships to arrive at our final ship number. (Numbers are rounded for simplicity's sake)

Fictional "Imperial-Class" Battleship

**Length:**1521ft(463.60m)

**Beam:**283ft(86.25m)

**Height:**337ft(102.71m)

**Crew Complement:**5261

**Imperium vs Fictional**

So, as you can see above, we have arrived at our final numbers for an 'Imperial-Class' Supership. Now, to fully see how they would stack up vs an Imperium Battleship, we have to increase the scale of our supership to the scale of an Imperium Battleship. The question is... just how big IS an Imperium Battleship? This is where we run into a bit of an issue. I don't own any of the rulebooks that might give us exact numbers, but I was able to find a thread where it was stated that an Emperor-Class was 6km long, with a Crew Complement of 18,000 to 24,000 men. We'll split the difference at 21,000. Using these numbers as an example, we can then figure out what our Imperium ship might be.

**Length:**19685.04ft(6000m)

**Beam:**???

**Height:**???

**Crew Complement:**21,000

Unfortunately, it's impossible to determine just how large an Imperium ship is, as we are missing stats for the Beam and Height of the ship. However, just to have numbers, we CAN compare the Length of our fictional ship to the Beam and Height, determine the difference, and then apply this to our Imperium ship to have numbers to compare with. Using this method, we can arrive at:

**Beam:**3666ft(1117m)

**Height:**4364ft(1330m)

This gives us the final statistics of our Imperium vessel at:

**Length:**19685ft(6000m)

**Beam:**3666ft(1117m)

**Height:**4364ft(1330m)

**Crew Complement:**21,000

Now, for the fun part: How does this compare to our Fictional vessel, upsized to a similar scale? With the exact measurements of both ships to compare with, we can scale up our fictional ship to Warhammer 40k size, which has been stated to be 1/43 scale. That gives us:

**Fictional Imperium-Scale Supership**

**Length:**65403ft(19934.8m)

**Beam:**12168ft(3708.75m)

**Height:**14490ft(4416.53m)

**Crew Complement:**230,000

Which means that, at the end of the day, Warhammer 40k is a bit underscaled if you were to compare two similarly-sized 'capital' ships of the line.

However, there IS actually a Warhammer ship of similar size to our scaled-up Supership:

http://warhammer40k.wikia.com/wiki/Glor ... Battleship

Generally speaking, each Space Marine chapter only fielded one of these ships, making them entirely unique, and each one was personalized to the Chapter fielding it. There are also Abyss-class ships that were fielded by the traitor legions. However, given that I was attempting to compare 'line' ship to Line Ship, I haven't made a comparison between these larger ships and our fictional Supership.

So, after all that, if you've bothered to read, what do you think? Have I screwed up my math somewhere? Is this around what you were expecting?

Thank you, and this took a lot longer than I thought it would.