GURPSよろず

　Scale is a race’s physical dimensions relative to the human baseline. This is expressed primarily by SM: A race that’s bigger than humans has a positive SM; one that’s smaller, a negative SM. Choice of scale affects largest dimension, ST, and weight and HP by the same number of steps. See the Size and Weight Table (above) for specifications.
　When using the table, largest dimension is usually rounded up to the next value shown; e.g., a 5’2” human is SM 0.
This should be applied to the race, not the individual; typical humans are SM 0, so a 6’4” human doesn’t have to be treated as SM +1.
　Weights shown are typical for the specified SMs, however. A human weighing 125 lbs. would probably be shorter than 6’; a 6’ human would probably be heavier than 125 lbs. For humanoids, use the Build Table (p. B18).

　Size Modifier should be adjusted for build: +1 for an elongated box shape, or +2 for a cube, sphere, or blob (p. B19). Adjustments in the other direction are also possible; e.g., a mature boa constrictor is 7’ to 10’ long (roughly SM +1), but weighs 22-33 lbs., a bit under the weight for SM -1, and so can be given a build modifier of -2 for an elongated cylinder shape.
　For humanoid races, use 0-point features to represent smaller adjustments to build:

　Gracile: Gracile 1 adds 5% to average height for a character's ST; Gracile 2 adds 10%. Weight is unchanged.

　Robust: Robust 1 subtracts 5% from average height for a character’s ST; Robust 2 subtracts 10%. Weight is unchanged.

　The standard GURPS approach to racial scale relies on a realistic principle: the square-cube law. If a race’s shape is kept the same but its longest dimension is doubled, its other two dimensions must also double; that multiplies its volume, and therefore its weight, by 2×2×2, or the cube of 2. On the other hand, its 体力 is doubled, and its Basic Lift is multiplied by 2×2, or the square of 2 (in proportion to the cross-section of its muscles). Using the Size and Weight Table (p. 13) gives results consistent with the square-cube law. Longest dimension, weight, 体力, and HP all have the same modifier for scale ――the racial SM.

　Examples: An average human being weighs 125 lbs., and has BL of 20 lbs., or 16% of their weight. A tarantula weighs about 2 ounces (0.125 lb.), giving it SM -6; based on this, it has 体力 1 and HP 1. Its BL is 0.2 lb., or 3.2 ounces, which is 160% of its weight! (To have the proportionate strength of a spider, you need to have the proportionate size of a spider.)

　To obtain exact scale values relative to SM 0 ――especially for races based on animals with known weights ――divide weight in pounds by 125 (or multiply weight in tons by 16) and use this as a weight multiplier. Take its cube root to find the multiplier for 体力, HP, and longest dimension. Figure SM from longest dimension.

Example: An Indian elephant averages 4.4 tons. Multiplying by 16 gives a weight multiplier of 70.4. Taking the cube root gives a 体力, HP, and length multiplier of 4.13, for 体力 41, HP 41, and length 25’ (SM +4).

　In the real world, scaling is even more complicated than the realistic approach assumes. To apply the square-cube law, we assumed that a man, or a tarantula, was exactly the same shape ――just bigger or smaller. In reality, large and small creatures are built differently. Small animals have delicate legs; large ones have massive pillars. There are entire books exploring this subject, creating mathematical models, comparing measurements of different creatures, or both!
　If you enjoy research and physics, there’s nothing wrong with doing detailed calculations of your invented races’ height, weight, strength, and speed. But for any animal between SM -6 (a tarantula) and SM +6 (an estimate for one of the largest land dinosaurs), the rules under Realistic Scale will be off by less than a factor of 2. You can guess at adjustments, making big creatures stronger and squatter, and small ones weaker and skinnier; or you can accept a lower standard of precision as close enough for a game. Whichever you choose to do, if you and your players are having fun, it isn’t wrong.

　Races in GURPS need not be realistic! Gigantic beings in epics such as the Odyssey, mock epics such as Gargantua and Pantagruel, or outright satires such as Gulliver’s Travels move and lift things just like human beings, despite the difference in scale; the same is true of creatures in movies, especially those played by human actors with the aid of rubber suits and miniature sets. (Both the Fifty-Foot Woman and the Incredible Shrinking Man moved like normal-sized people.) In many cases, scale isn’t consistently defined. Even writers who understand the square-cube law may choose to ignore it to tell a better story, as H.G. Wells (a trained biologist) did with the giant wasps, rats, and humans in The Food of the Gods.
　In cinematic or epic treatments of scale, tiny or huge beings interact with the environment in ways that are visually the same as for normal-sized ones. To achieve this, set aside the guidelines treating 体力 and HP as multiples of longest dimension. Instead, let them equal 2×, 4×, or 8× the square root of (weight in lbs./5), for creatures, machines, and continuous masses of material, respectively. Applied to a human-shaped creature, this gives BL equal to 16% of weight, regardless of scale. Similarly, multiply all Move scores by the scale factor (cube root of the weight multiplier); this gives 基本移動力 equal to 2.5× the longest dimension in yards, regardless of scale.

　Some life forms or machines are small enough that they effectively have 体力 0. A living organism weighing 0.25 ounce (0.016 lb.) would have 体力 0.5, rounding up to 1. Anything smaller would usually be unable to take effective physical action, not to mention being tiny (SM -8 for life forms). They would be unlikely to make suitable player-character races or interesting adversaries.
　There’s a way around this: treating a swarm of tiny entities as a single character with a 種族テンプレート. The primary trait for this is 「負傷耐性」 (「集合体」) (p. 43). Other traits depend on the size of the swarming entities. This represents being a swarm all the time. The ability to become a swarm is 「変身」 (Shapeshifting, pp. 38-39).

● Small entities down to SM -8 (from 3.5” for typical animals to 1.8” for cubical or spherical objects) have the 特色 「群れの体」 (p. 12). They normally have 体力 0.5 (rounding up to 1) or better; individuals can perform some effective physical actions.

● Tiny entities down to SM -20 (the size of a flea or a sand grain) have Body of Swarm and the modifier 「L-浸潤」 (p. 43). Individuals have negligible 体力.

● Microscopic entities (such as single cells, nanites, or fog droplets) are too small to be seen or to perceive the macroscopic world; treat them as constituents of a single 集合体 being, without 「群れの体」.
　The number of small entities that make up a swarm can be estimated as the square of (HP of swarm / HP of separate bodies). The HP of separate bodies should be less than 1/3 of swarm HP; any larger and there would be too few to make up a “swarm.” Tiny and microscopic entities don’t need to be counted or assigned an exact size.
　With 「L-散在」 (p. 43), a swarm can disperse its component bodies over a wide area. While dispersed, it’s effectively insubstantial.