# Starship Length, Volume and Mass

### General Discussion

 5 people marked this as a favorite.

Let's say your average starship is about five times as long as it is tall and wide.

A starship's density should be about 0.25 metric tons per cubic metre. A jet airliner has an average density of 0.27, but 0.25 is a nicer number to work with for approximations.

So for the above starship with proportions of 5:1:1, to calculate its total mass in metric tons, all you need is:

m = l³ / 100

Where l is the ship's length in metres along its longest axis. If you start with the mass and want length, it's the same thing in reverse:

l = ∛(m * 100)

 1 person marked this as a favorite.

That's interesting. I grew up on Traveller, so I'm used to their version of tonnage, where a 3m cube of space is 2 helium tons. Because that's how much it displaces helium. Or was it hydrogen? I forget.

 1 person marked this as a favorite.

A 3m cube of 2 tons is equal to about 0.22 tons/cubic metre. Pretty close!

 1 person marked this as a favorite.
Pathfinder Adventure Path, Rulebook, Starfinder Roleplaying Game Subscriber

That's a pretty darn nice and simple ratio to use, UR. I'd actually expect a slightly higher density than in an aircraft, but ease of maths means I'm happy to handwave it.

 1 person marked this as a favorite.

Useful points of reference:

1 cubic metre of water is 1 metric ton (tonne).

1 cubic metre of air is 0.0013 metric tons.

1 cubic metre of solid steel is 7.8 metric tons.

1 cubic metre of bone is 1.85 metric tons.

 1 person marked this as a favorite.
Odraude wrote:
That's interesting. I grew up on Traveller, so I'm used to their version of tonnage, where a 3m cube of space is 2 helium tons. Because that's how much it displaces helium. Or was it hydrogen? I forget.

Wasnt it Hydrogen since that is the most basic atom and acts as a decent universal measuring point?

 1 person marked this as a favorite.

I've seen similar discussions on the "Atomic Rockets" web site.

They propose using a design more akin to a nuclear submarine than air craft for determining 'ship density'. Since a submarine has to withstand greater and repeated pressure variances.

Yes, I understand a star ship is invariably only experianceing an atmorpheric difference of about one atmosphere to nill and back per trip... but still, you'd want serious redundancy in something that might pop a leak half way between places in the middle of nothing.

 1 person marked this as a favorite.
, wrote:

I've seen similar discussions on the "Atomic Rockets" web site.

They propose using a design more akin to a nuclear submarine than air craft for determining 'ship density'. Since a submarine has to withstand greater and repeated pressure variances.

Yes, I understand a star ship is invariably only experianceing an atmorpheric difference of about one atmosphere to nill and back per trip... but still, you'd want serious redundancy in something that might pop a leak half way between places in the middle of nothing.

Yep, in many regards underwater engineering is a lot harder than space systems engineering -- and that's one of the main reasons. The pressure goes up *very* quickly as you get deeper underwater. The direction of the pressure's easier to work with underwater than in space, but the magnitude's the killer.

 1 person marked this as a favorite.
Umbral Reaver wrote:
Let's say your average starship is about five times as long as it is tall and wide... A jet airliner has ...

Keep in mind that a cylindrical shape matters far less outside an atmosphere, unless you need to worry about aerodynamics or presenting a small cross-section (stealth and/or combat) a sphere's far better.

 1 person marked this as a favorite.

I know that spheres are better, but I'm going by most common science fiction ships, which tend to be longish.

 1 person marked this as a favorite.
Callum Finlayson wrote:
Umbral Reaver wrote:
Let's say your average starship is about five times as long as it is tall and wide... A jet airliner has ...
Keep in mind that a cylindrical shape matters far less outside an atmosphere, unless you need to worry about aerodynamics or presenting a small cross-section (stealth and/or combat) a sphere's far better.

Or keeping the engines far away from the crew members...

 1 person marked this as a favorite.

If I recall, I believe that rocket propelled 'sky scrapers' are pretty good for a 'burn and turn' ship. Since the ship can go about 1G, it can replicate Earth gravity. So the ships are built more like buildings, where the ceiling is facing the nose of the fuselage and the floor is directed towards the rear. Something like the ships from The Expanse.

 1 person marked this as a favorite.
Umbral Reaver wrote:
A starship's density should be about 0.25 metric tons per cubic metre. A jet airliner has an average density of 0.27, but 0.25 is a nicer number to work with for approximations.

Knowing nothing about... well anything even tangentially related to starship engineering why is that the density it should be? Is it a "humans and their stuff and their air take up so much space and have so much mass" sort of thing?

 1 person marked this as a favorite.
Pathfinder Adventure Path, Rulebook, Starfinder Roleplaying Game Subscriber
pocsaclypse wrote:
Umbral Reaver wrote:
A starship's density should be about 0.25 metric tons per cubic metre. A jet airliner has an average density of 0.27, but 0.25 is a nicer number to work with for approximations.
Knowing nothing about... well anything even tangentially related to starship engineering why is that the density it should be? Is it a "humans and their stuff and their air take up so much space and have so much mass" sort of thing?

Pretty much, yes. People need a certain amount of room (and air), and bulkheads and cables and doors and things need a certain amount of room and when you factor in all of the things together, the overall density of the container needed to cart all of those things around is "a number". I'd have to look it up to make sure UR is correct, but I have no reason to doubt that figure (it's in the right order of magnitude for sure).

 1 person marked this as a favorite.
Chemlak wrote:
Pretty much, yes.

You ever do that thing where in the process of asking a question you realize that youve answered it? I realized too late after posting that yes actually, how much stuff we have in a certain amount of space is the literal definition of density. *face palm*

 1 person marked this as a favorite.

Extra complexity if you even care! It probably doesn't matter:

If your ship is much narrower than a 5:1:1 box, reduce the total mass by an appropriate amount. Does your ship take up about half that volume? Halve the mass from the equation.

If your ship is much wider and/or taller, increase the mass accordingly. It's probably not important to get an accurate measurement at all.

 1 person marked this as a favorite.

i love this, you just dont know how much i really love this. when people throw out math and other fun stuff i just grin.Although i almost killed one of my old DMs for using a moving bird as a point of origen. every round i would wonder why my math wasnt adding up a cart a hill and the enemys would change in distance. so i asked....wish i hadnt.BTW i only gave him a hard time cause he swore up and down he was smarter than us and was a rules lawyer. ok that was a bit must to say i lvoe when people use math but hey.

 Community / Forums / Starfinder / Starfinder General Discussion / All Messageboards Forums       Paizo             General Discussion             Customer Service             Product Discussion             Website Feedback             PaizoCon                   General Discussion                   Events                         Organized Play                         Paizo Events                         Third-Party and Fan Events             Community Use             Licensed Products                   General Discussion                   Comics                   Digital Games                         Pathfinder: Kingmaker                         Pathfinder Online                   Miniatures       Pathfinder             Pathfinder Second Edition                   General Discussion                   Advice                   Rules Discussion                   Advanced Player’s Guide Playtest                         General Discussion                         Investigator Playtest                         Oracle Playtest                         Swashbuckler Playtest                         Witch Playtest                   Paizo Products                   Third-Party Pathfinder RPG Products                         Advice and Rules Questions                         Product Discussion                   Conversions                   Homebrew and House Rules             Lost Omens Campaign Setting                   General Discussion                   Lost Omens Products             Pathfinder Adventure Path                   General Discussion                   Age of Ashes                   Tyrant's Grasp                   Return of the Runelords                   War for the Crown                   Ruins of Azlant                   Ironfang Invasion                   Strange Aeons                   Hell's Vengeance                   Hell's Rebels                   Giantslayer                   Iron Gods                   Mummy's Mask                   Wrath of the Righteous                   Reign of Winter                   Shattered Star                   Skull & Shackles                   Jade Regent                   Carrion Crown                   Serpent's Skull                   Kingmaker                   Council of Thieves                   Legacy of Fire                   Second Darkness                   Curse of the Crimson Throne                   Rise of the Runelords             Pathfinder Adventures             Pathfinder Accessories             Pathfinder Adventure Card Game                   General Discussion                   Rules Questions and Gameplay Discussion                   Homebrew and House Rules             Pathfinder First Edition                   General Discussion                   Advice                   Rules Questions                   Paizo Products                         Product Discussion                         Beginner Box                   Pathfinder Player Companion                   Third-Party Pathfinder RPG Products                         Product Discussion                         Advice and Rules Questions                   Conversions                   Homebrew and House Rules       Starfinder             Starfinder General Discussion             Advice             Rules Questions             Homebrew             Starfinder Adventure Path                   General Discussion                   Attack of the Swarm                   Dawn of Flame                   Signal of Screams                   Against the Aeon Throne                   Dead Suns             Starfinder Accessories             Third-Party Starfinder Products       Organized Play             Pathfinder Society             Pathfinder Society Playtest             Starfinder Society             Pathfinder Adventure Card Society             GM Discussion             Events                   Local Play                   Online Play       Streaming & Actual Play             General Discussion             Pathfinder                   General Discussion                   Knights Of Everflame                   Oblivion Oath                   Pathfinder Fridays                   Third-Party Broadcasts             Starfinder                   General Discussion                   Starfinder Wednesdays                   Third-Party Broadcasts       Online Campaigns             General Discussion             Recruitment             Play-by-Post             Play-by-Post Discussion       Gamer Life             General Discussion             Gaming                   Campaign Journals                   D&D                         3.5/d20/OGL                         4th Edition                         5th Edition (And Beyond)                   Other RPGs                   Miniatures                   Card & Board Games                   Gamer Connection             Entertainment                   Artwork & Crafting                   Books                   Comics                   Movies                   Music & Audio                   Technology                   Television                   Video Games             Forum Games             Off-Topic Discussions       Archive             Paizo                   Books & Magazines                         Planet Stories®                         Dragon Magazine                               General Discussion                               Dragon Compendium                               Dragon and Dungeon Transition Discussion                         Dungeon Magazine                               General Discussion                               Savage Tide Adventure Path                               Age of Worms Adventure Path                               Shackled City Adventure Path                               Maure Castle                   Paizo Games                   RPG Superstar™                         General Discussion                         Previous Contests                               RPG Superstar™ Season 9 (2016)                                     Open Call: Design a wondrous item, magic armor, or magic weapon                                     Round 2: Create an encounter map                                     Round 3: Create a Bestiary entry                                     Round 4: Design an encounter                                     Round 5: Submit an adventure proposal                               RPG Superstar™ 2015                                     Open Call: Design a magic armor, weapon, ring, rod, or staff                                     Round 2: Create a map                                     Round 3: Create a Bestiary entry                                     Round 4: Design an encounter                                     Round 5: Submit an adventure proposal                               RPG Superstar™ 2014                                     Open Call: Design a wondrous item                                     Round 2: Create a Bestiary entry                                     Round 3: Design an encounter                                     Round 4: Submit an adventure proposal                               RPG Superstar™ 2013                                     Open Call: Design a wondrous item                                     Round 2: Design an archetype                                     Round 3: Create a Bestiary entry                                     Round 4: Design an encounter                                     Round 5: Submit an adventure proposal                               RPG Superstar™ 2012                                     General Discussion                                     Open Call: Design a wondrous item                                     Round 2: Create a new organization                                     Round 3: Create a Bestiary entry                                     Round 4: Design an encounter                                     Round 5: Submit an adventure proposal                               RPG Superstar™ 2011                                     General Discussion                                     Open Call: Design a wondrous item                                     Round 2: Design an archetype                                     Round 3: Design a villain                                     Round 4: Create a Golarion location                                     Round 5: Submit an adventure proposal                               RPG Superstar™ 2010                                     General Discussion                                     Open Call: Design a wondrous item                                     Round 2: Create a monster concept                                     Round 3: Create a Bestiary entry                                     Round 4: Design a Golarion location                                     Round 5: Submit an adventure proposal                               RPG Superstar™ 2009                                     General Discussion                                     Open Call: Design a wondrous item                                     Round 2: Create a villain concept                                     Round 3: Create a villain stat block                                     Round 4: Design a villain's lair                                     Round 5: Submit an adventure proposal                               RPG Superstar™ 2008                                     General Discussion                                     Open Call: Design a wondrous item                                     Round 2: Design a country                                     Round 3: Design a villain                                     Round 4: Design thematically linked monsters                                     Round 5: Design an encounter                                     Round 6: Submit an adventure proposal                   Game Space             Starfinder                   Character Operations Manual Playtest                         General Discussion                         Biohacker                         Vanguard                         Witchwarper             Pathfinder                   Playtests & Prerelease Discussions                         Pathfinder Playtest                               Pathfinder Playtest General Discussion                               Game Master Rules                                     Magic Items                                     Monsters and Hazards                                     Running the Game                               Player Rules                                     Ancestries & Backgrounds                                     Classes                                     Creating a Character                                     Playing the Game                                     Skills, Feats, Equipment & Spells                               Playtest Feedback                                     Doomsday Dawn Game Master Feedback                                     Doomsday Dawn Player Feedback                                     Pathfinder Society Scenario Feedback                               Pathfinder Playtest Prerelease Discussion                         Ultimate Intrigue Playtest                               General Discussion                               Playtest Feedback                         Occult Adventures Playtest                               General Discussion                               Rules Discussion                               Playtest Feedback                         Advanced Class Guide Playtest                               General Discussion                               Playtest Feedback                               Class Discussion                         Mythic Adventures Playtest                               General Discussion                               Player Feedback                               GM Feedback                               Adventure Feedback                         Advanced Race Guide Playtest                         Ultimate Combat Playtest                               Playtest Results: Round 1                               Playtest Results: Round 2                               Gunslinger Discussion: Round 1                               Ninja Discussion: Round 1                               Samurai Discussion: Round 1                               Gunslinger Discussion: Round 2                         Ultimate Magic Playtest                               Announcements and General Discussion                               Round 1: Magus                               Round 2: Words of Power Playtest                               Round 2: Words of Power Discussion                               Round 3: Revised Magus Playtest                               Round 3: Revised Magus Discussion                         Advanced Player's Guide Playtest                               General Discussion                               Round 1: Cavalier and Oracle                               Round 2: Summoner and Witch                               Round 3: Alchemist and Inquisitor                               Advanced Player's Guide Playtest: Final Playtest                         Pathfinder Roleplaying Game                               Announcements                               Playtest Reports                               General Discussion (Prerelease)                               Design Forums                                     Open Comments                                     Magic Items                                     High Level Play                                     Additional Rules                                     Magic and Spells                                     Combat                                     Equipment and Description                                     Prestige Classes                                     Skills and Feats                                     Classes: Sorcerer and Wizard                                     Classes: Bard, Monk, and Rogue                                     Classes: Cleric, Druid, and Paladin                                     Classes: Barbarian, Fighter, and Ranger                                     Ability Scores and Races                               Alpha Playtest Feedback                                     General Discussion                                     Alpha Release 3                                           General Discussion                                           Races & Classes                                           Skills & Feats                                           Combat & Magic                                           GM Tools                                           New Rules Suggestions                                     Alpha Release 2                                           General Discussion                                           Races & Classes                                           Skills & Feats                                           Combat & Magic                                           GM Tools                                           New Rules Suggestions                                     Alpha Release 1                                           General Discussion                                           Races & Classes                                           Skills & Feats                                           Combat & Magic                   Pathfinder Society Scenario Submissions                   Pathfinder Society Roleplaying Guild Faction Talk                         Dark Archive                         The Exchange                         Grand Lodge                         Liberty's Edge                         Scarab Sages                         Silver Crusade                         Sovereign Court                         Retired Factions                               Andoran                               Cheliax                               Lantern Lodge                               Osirion                               Qadira                               Sczarni                               Shadow Lodge                               Taldor                   Pathfinder Tales Want to post a reply? Sign in.