We really don't have that many hard “facts” on how big the Imperial Navy is in Star Wars; other than a few key phrases.

1. Zahn's Specter of the Past: “A thousand systems left, out of an Empire that had once spanned a million. Two hundred Star Destroyers remaining from a Fleet that had once included over twenty-five thousand of them.”

2. WEG Imperial Sourcebook: “A Sector Group can be expected to contain at least 2,400 ships, 24 of which are Star Destroyers, and another 1,600 combat starships. Thousands of Sector Groups are at the Emperor’s command as he seeks to bring the galaxy firmly under his control.”

If we use Zahn's “25,000 Star Destroyers” figure, the Empire had at least 1,041 sector group equivalents; making for a total of 1.6~ million combat starships in the Imperial Navy.

There are a few more tricks we can use to get a finer “hack” to estimate the masses and numbers of unknown ships from that simple datapoint.

During WWII, the USN built about 10.3~ million metric tons of combatant shipping, which was broken down as:

A lot of these categories don't neatly line up; due to differences in translating from a “wet navy” to “space navy”, but we can make a guess as:

The reason for Carriers/Transports being so large as a category, is that while in SW; the role of fleet/fast carriers is mostly taken over by all categories of warships capable of operating starships due to repulsorlifts allowing effortless VTOL flight...there's still a need for some sort of small carrier to do the following roles:

• Supplementing convoy defense forces with extra TIE Fighters to protect from rebel fighter attack.

• Supplementing Imperial planetary assaults.

• Transporting small craft and small ground units to and fro within the Empire -- replacement TIE fighters are flown off them to replace combat losses on Star Destroyers after an engagement, etc.

In 1945, the USN had an entire fleet unit attached to the Pacific Fleet called CARRIER TRANSPORT SQUADRON, PACIFIC FLEET which contained 26 escort carriers that did nothing but shuttle combat aircraft and other items to forward bases from Hawaii/Continental United States.

Even with hyperdrives, it would take time for things to be delivered – since they talk in Solo about how expensive refined Hyperdrive fuel is -- it may be much more economical (even for the Empire) to have replacement TIEs and replacement crew members delivered on slow ships (taking a week to transit the galaxy instead of the Millennium Falcon's "hours to any place")

Estimating Masses of Star Wars Vehicles/Ships

There are a few known datapoints we can generate from the films:

Millennium Falcon

The Millennium Falcon (as of Empire) has 7 landing gear leg pads as shown in the ventral view below:

Red is ANH-era landing gear – Blue extra legs added by ESB-era.

Scaling off known rough dimensions for the Falcon gives me dimensions of 137 x 133 cm (1.821 m2) for each landing gear.

A lot of traditional “rules” for vehicle mobility don't apply thanks to repulsorlifts in Star Wars; because you don't need the ground surface to hold up under the horizontal shear of the vehicle dragging itself forward like you would a traditional vehicle.

Treating the Falcon's landing gear as footings; and checking a ground bearing capacity table, we get the following masses for the Falcon:

Interestingly, WEG's stats for the Falcon say it can carry 100 metric tons of cargo; meaning that maybe WEG did do some basic volumetric calculations back in the 1980s.

One possible reason why Han added two more landing gear legs to the Falcon between ANH and ESB is that before the events of A New Hope, he basically flew the Falcon out of spaceports, with the occasional side jaunt to impromptu landing strips that were carefully chosen for smuggling, whereas when he started working with the Rebellion after the events of A New Hope, he needed to go to places really off the beaten path with little prep time available; so he had it modified to add more landing gear to reduce his ground pressure.

While you could use repulsorlifts to enable landing the Falcon on totally unsuitable surfaces, the energy signature from keeping them running would be quite detectable, making it bad for smuggling use.

With a volume of 1716 m3 for the Falcon [ST vs SW Net (Volumetrics I) – LINK] the density of the Falcon comes out to 194.75 kg/m3 (5 leg gear) or 272.72 kg/m3 (7 leg gear); for an average of 233.74 kg/m3.

X-Wing

X-Wing, Temple Hangar, A New Hope

Doing some scaling off the known length (12.5 meters) given in multiple sources; I get the following approximate sizes for the landing gear skids:

Front landing gear skid: 70 x 26 cm (0.182 m2)
Rear Landing Gear skid: 65 x 33 cm (0.2145 m2 each)
Total landing skid area: (0.611 m2)

Consulting our trusty table for soil bearing capacity, we get:

The reason for not having rock or gravel soils (which have significantly increased bearing capacity) in the table is because of this scene from Empire:

Empire Strikes Back, R2D2 repairs the X-Wing following Yoda's Force Lift

You'll notice that the ground the X-Wing is sitting on is by definition, heavily waterlogged, yet it's strong enough to support the X-Wing without it sinking into the ground.

All this tends to support the old canon mass (10 metric tons) the X-Wing; once again proving that maybe WEG did do their math at some point.

With a volume of 27 m3 for the X-Wing [ST vs SW Net (Volumetrics I) – LINK] and using a mass of 10,000 kg; the density of the X-Wing comes out to 370.37 kg/m3.

AT-AT

Back in the old days, Curtis Saxton at his “Military Walkers” website (LINK) estimated the AT-AT's critical dimensions as 22.6±0.8m high; ~26m long; ~7.9m wide (hull).

Doing some scaling off an Empire Strikes Back frame:

and assuming the AT-AT is 23~ meters high, I get an estimate of AT-AT foot diameter being 4.14m; giving me a surface area for each AT-AT “foot” of 13.46 meters.

Saxton noted that only one foot moves at a time for the AT-AT's walking motion, giving us three legs in contact at any one time.

Unlike our prior repulsorlift examples (Falcon/X-Wing), the AT-AT has to deal with the horizontal shear of the soil. Another constraint is that the AT-AT's in Empire crossed a heavy snow-filled glacier without an appreciable degradation in mobility; limiting the maximum ground pressure to about 14 PSI (9,843~ kg/m2) – or about 87.5% the ground pressure of a Human (16 PSI / 11,249.1 kg/m2).

With this, we end up with a low end (3 leg contact) mass of 397,460 kg and high end (4 leg contact) mass of 529,947 kg; with each leg exerting 100 to 130 metric tonnes of force.

This explains how an AT-AT was able to easily crush Luke's snowspeeder in Empire; and how it was able to shrug off light blaster fire from the snow speeders; since it's heavier than a YT-1300 freighter (we earlier estimated the Falcon's mass as about 400~ tonnes).

With a volume of 615 m3 [ST vs SW Net (Volumetrics I) – LINK]; the AT-AT's density is 646.27 kg/m3 (3 leg contact) or 861.7 kg/m3 (4 leg contact).

This is significantly denser than the Falcon or X-Wing; but far below the density of modern AFVs. I believe that this is due to Imperial requirements (AT-AT ICS Image) that the AT-AT be a sealed environment vessel, supporting 40 men for however long in extreme environments, forcing a fairly large internal volume so people can live in the AT-AT for a long period of time.

NOTE: Alternately, the AT-AT may weigh 633.4 metric tons if we arbitrarily give it a density of 1030 kg/m3; making it slightly heavier than water – enabling AT-AT's to “walk” across a river-bed instead of simply floating across.

Known “Outfit Densities”

In Naval Architecture/Engineering, the density of a ship is known as the “outfit density”, shown by this graph from US Naval Sea Systems Command (LINK). Known or Estimated Outfit Densities are:

If you use the above table for guidelines and combine it with some volumetrics from ST vs SW net; we get:

When you look at the old “Legends” canon for cargo capacity; you get the following table when combined with our estimated masses:

It makes it clear that the Lambda-class is designed more for intra-system or short range hyperspace cargo hops; rather than being a long distance cargo hauler like the CR-90 or YT-1300 are.

A lot of these numbers keep “sanity checking” quite well, which makes me wonder once again about WEG's system for generating numbers for their RPG.

Estimating Starship Numbers

Now that we have some crude masses for various Star Wars ships, we can figure out the total fleet numbers.

We know that there were 25,000 ISDs and we've estimated they mass 2.78E10 tonnes per ship, for a total of 6.95E+14 tonnes in Star Destroyers.

If we assume that 20% of the total fleet tonnage was devoted to Capital Ships (Star Destroyer/Cruiser/Dreadnought); and that 70% of that Capital Tonnage was devoted to Star Destroyers (14% of total tonnage), dividing 6.95E14 by 14% gets us a total Imperial Fleet mass of 4.96E15 tonnes; which we can then apply in the table below: (Or you can use this Excel Spreadsheet -- or this online HTML interactive calculator)

This may sound pretty crazy, particularly the smaller craft numbers (billions of ships!), but when you look at the sheer scope of Star Wars, it's pretty low when you look at the old canon – Star Wars: The Essential Atlas, Daniel Wallace & Jason Fry (2009) has the following bullet point:

“Do the math and you wind up with about 7.1 billion habitable stars in the known galaxy—that's about 3.2 billion habitable star systems. We haven't gotten everywhere yet—it's estimated that nearly a billion of those systems actually have someone living in them. But most of those places are pretty lonely—if I'm remembering my census data correctly, about 69 million of those systems meet the population requirements for Imperial representation, and just 1.75 million planets are full member worlds.”

That comes down to a figure of:

0.39 Cruisers
4.63 Destroyers
2,857 Frigates
13,142 Corvettes
7,200 System Patrol Craft

average for a typical “full member world”.

It gets worse if you consider a “lightly populated sector” – such as Chommell Sector, which contains Naboo. According to Attack of the Clones: Incredible Cross Sections, Curtis Saxton, (2002), there are 36 full member worlds there, giving us the following average numbers for that sector:

14 x Cruisers
167 x Destroyers
102,857 x Frigates
473,143 x Corvettes
259,200 x System Patrol Craft

That's a lot, right? Well, according to the AOTC:ICS, Chommel sector also contains 40,000 settled dependencies and 300 million empty stars. If we limit ourselves to just the settled dependencies; we end up with:

2.57 x Frigates
11.8 x Corvettes
6.48 x System Patrol Craft

on average for every dependency. And to make things worse, some craft like System Patrol Craft (SPCs) don't have hyperdrives, or they're relatively short-ranged.

Further complicating strategic planning for any naval planner in Star Wars is the Hyperdrive.

It effectively means a heavy concentration of enemy craft could immediately appear over your world(s) at any time – strategic defenses such as fortifications or coastal defenses simply don't exist in the context of Star Wars, unless your world(s) are in an area of space with a large amount of natural hazards (The Maw).

Thus, the only way to assuredly protect against pirate raids is to have warships at the ready, already formed into task groups near strategic locations. Defensive tasking can quickly run down a large force by frittering it away in defensive deployments until there's not enough ships left over to form a significant mass capable of overcoming enemy resistance in an offensive action.

All the more so if local governors and leaders demand that you execute anti-piracy or anti-smuggling duties as collateral to your standard defense duties.

Star Wars Ship Sizes

A lot of people keep getting tripped up by the old Legends canonicites as well as semantics concerning the name “Star Destroyer”.

An Imperial-class Star Destroyer is only 1.6 km long; and there's tons of other ships in the old SW continuity that are as big or bigger:

• Corporate Sector Authority Invincible-class Dreadnaught – 2 km long, very very old.

• Kuat Defense Fleet's Mandator-class Star Dreadnought – 8 km long, in service 20 years before Phantom Menace.

It's clear that Star Wars technology isn't as frozen in stasis as some believe; but it's also not as fast moving as our 20th century was.

I think a good analogy might be that technological development in Star Wars is moving at the pace of the pre-industrial revolution, now that thousands of years of galactic civilization have existed; and all the “easy hanging fruit” have been harvested in technological development.

In the Age of Sail, ships lasted for decades – from when she was ordered to the the Battle of Trafalgar, it was 47 years for HMS Victory; and we're seeing that length of service slowly return again with ships approaching 40-50 years of service in the USN.

In Star Wars the major causes of ship destruction -- corrosion and constant non regular flexure of the frame from the sea -- aren't an issue and lives in centuries could easily be obtained, which would retard the pace of technological advancements. As a result, you'd have a lot of older multi-kilometer class ships that were bought centuries ago for local defense fleets that haven't been scrapped yet.

Another issue might be hyperspace travel costs. In the old Legends canonicity, hyperdrives had been in existence for 25,000 years – but there may have been an exponential function involving mass – translating a certain amount of mass into hyperspace and back over a fixed mass limit causes energy requirements to skyrocket. Over 25,000 years, that fixed mass limit has slowly been pushed rightwards; enabling bigger and bigger ships over time, but it's still there.

This brings to mind an amusing thought that the energy cost needed to push the first Death Star through hyperspace from Scarif to Alderaan may have been more “expensive” than it was to actually fire the Superlaser at Alderaan – explaining why everyone was so befuddled by the existence of the Death Star in A New Hope – they weren't expecting a moon sized battlestation over Alderaan; but they were common elsewhere in the galaxy as local defense stations, etc. (Coruscant habitat stations).

This hyperdrive exponential function might also explain how small-time smugglers like Han Solo can make money off ships that only have a 100 tonne payload capacity – even the Falcon's temperamental engines might sip hyperdrive fuel at an economical enough rate (compared to larger bulk ships) that small YT-1300s can serve out of the way places that aren't big enough to justify the cost of a full size Black Ice-class cargo carrier (7.8 km long, 1 billion tons cargo).

Returning back to the Imperial-Class Star Destroyer – the ISD forms the backbone of the Empire's “Capital” fleet – as it's big enough to be able to overwhelm anything smaller than it, per WEG:

• “There are whole star systems whose gross domestic product is less than the cost of a single Imperial Star Destroyer. There are whole nations which, throughout their entire history, do not use as much energy as an Imperial expends to make a single hyperspace jump.” – Imperial Sourcebook.

• “The Imperial Star Destroyer has enough firepower to reduce a civilized world to slag or take on a fleet of lesser enemy vessels. Each carries a full stormtrooper division, complete with assault craft and ablative heat shields for orbital drops.” – Imperial Sourcebook.

• “A Star Destroyer is considered a line in itself. A naval staff study concluded that a Star Destroyer was the equivalent of at least the squadrons [14 to 60 ships] of the time, and would be more properly categorized as such. The Admiralty agreed with the analysis, but disagreed with the conclusion. The Admiralty felt that as there were more lines than squadrons, designating the Star Destroyer as a line unit would get them more Star Destroyers. The Admiralty’s thinking prevailed.” – Imperial Sourcebook.

It hits the “sweet spot” for the Empire:

• Small enough to be procured in large enough numbers – 25,000 – to make a significant dent in the Navy's requirements. If the same equivalent mass (6.95E14 tonnes) of Star Cruisers had been procured, there would only be 9,600 ships, likewise, for Star Dreadnoughts, only 138.

• Big enough to deal with the majority of offensive mission taskings that the Empire has, from anti-piracy operations, fleet actions to subjugation of rebellious planets without requiring additional aid beyond a couple of screening vessels since it has enough firepower to sweep aside the typical flotillas a rebellious planet or pirate group would have.

• Flexible – A Star Cruiser is about 2.6 times heavier, and probably three times more powerful than an Star Destroyer; but the Star Cruiser can only be in one place at a time; whereas it's equivalent in Star Destroyers can be three places at once. If there's a mission tasking that's greater than what a single Star Destroyer can handle; form an ad-hoc task force of multiple Star Destroyers to handle it, and then dissolve the Task Force later.

• Economical – if we're using the “mass = exponential function for hyperdrive energy requirements” theory, then it's significantly cheaper for the Empire to send a hundred Star Destroyers to smash a heavily fortified planet than it is to send a Star Dreadnought; due to hyperspace fuel costs.

So where are the big ships?

Han Solo himself says in Return of the Jedi:

“Now don't get jittery, Luke. There are a lot of command ships.”

So where are they, besides the Executor? Why are they being built if they're so uneconomical?

• If we use the “mass = exponential function for hyperdrive energy requirements” theory, then the majority of Star Cruisers/Star Dreadnoughts built were held in fixed reserve fleets protecting incredibly important locations like: Coruscant, Corellia, Fondor, Kuat, and Rendili as those locations are either the Imperial capital or major shipyards; keeping operational costs low due to little use of their hyperdrives. Their massive firepower and shielding would deter any potential assault.

• There are political limits on their use. In the old Legends canon, the Republic placed limits on the performance and range of the hyperdrives on the Kuat Defense Fleet's Mandators to prevent them from being used by Kuat to project massive firepower on a galactic range. Palpatine doesn't dissolve the Imperial Senate until just before Yavin, some nineteen years into his reign. While the Death Star Project was done in near absolute secrecy, it's kind of hard to hide the construction of Star Dreadnoughts from the Imperial Senate as they'd be constructed at known shipyards.

• Construction of such excessively large ships is actually a “prestige” project for the shipbuilders (Fondor, Kuat, Rendili, etc), to keep the technical knowledge on how to build extremely large warships alive; and to keep shipbuilders' names in the press, so that shipbuilders can try “upselling” Imperial military staffers on the latest designs they have – “All of these concepts have been proven in the Vincible Star Dreadnought, now in service with the Kuat Defense Fleet, my dear Admiral.”