Is there a correlation between size and speed?

[Greywander]

My intuition says bigger things move faster and smaller things move slower. However, after some brief research into the topic, speed and size seems to be all over the place. I was hoping to come up with a general rule for base speed based on size, but I don't know that that will work.

A lot of the mechanics of my system are still up in the air, but I thought I'd borrow a bit from D&D 5e. For now, I'm thinking a round will be about 6 seconds, and squares/hexes will be 1 yard in length (rather than 5 feet). This conveniently lets me express distances and ranges in yards, which is the same as the number of squares/hexes, and also easily converts to metric by swapping yards for meters. Creatures will be able to move up to their walking speed and take another action on their turn, and can use that action to sprint to cover more distance. So walking speed will be expressed in terms of yards per 6 seconds.

Now, a human apparently has a preferred walking speed of about 8 yards per round (a nice number which fits pretty closely to what you see in many tactical RPGs), or 4 feet per second. Dogs, who would be one size category smaller than humans... also have a walking speed of about 8 yards per round. Cats, who would be one size category smaller than dogs... also have a walking speed of 8 yards per round. Horses, who would probably be one size category larger than humans, have a walking speed of... 12 yards per round (6 feet per second)? I almost want to say that the default base walking speed is 8 yards, with some creatures (like horses) getting a faster or slower speed, but I know this won't hold true at very small sizes (ants, for example), and suspect it won't hold true for very large animals, either. More likely, speed scales with size, and dogs and cats are special cases who are faster than normal for their size.

Sprinting speed gets even worse. Average running speed for humans seems to be about 15 mph, according to my searches, perhaps pushing 20 mph for faster people (Usain Bolt managed to get close to 30 mph, but that would be for a character with maxed out stats for sprinting). Cats seem to have a sprinting speed of around 30 mph already, while elephants seem to vary from 11 mph to 25, depending on who you ask.

My thought for sprinting was for you to be able to sprint at an increment of your walking speed (or of some speed stat), but at the cost of some kind of resource, like stamina. So, in addition to moving your normal walking speed, if you also sprint your walking speed, then it costs 1 stamina. If you sprint twice your walking speed, it costs 2 stamina. 3 times your walking speed is 3 stamina. Etc. So running slower lets you cover more distance for less stamina cost. Sprinting speed would probably have a cap bases on what creature you are. So something like a cheetah would have a high sprint cap, but it would consume a lot of stamina to go that fast.

[Knaight]

Putting aside entirely immobile organisms for the moment, there's a correlation. It's really slight, lost in noise, and generally not worth considering as a general rule. The really slow large animals tend to be faster than the really slow small animals (large jellyfish vs. slugs), the really fast large animals tend to be faster than the really fast small animals (cheetah vs. rabbit), and that's definitely a trend line in between. Said trend is just lost in the noise unless you go really far, where even the fast single celled organisms are slower than the slow megafauna. For anything operating at the visible human scale a case by case approach is much better.

The default walking speed idea is also deeply dubious. Cats, dogs, and humans all tend towards similar speeds when walking, but diverge when running. Plenty of other animals in that same size range are nowhere close. For instance Komodo Dragons are right in that range, and they're pretty sluggish.

[Greywander]

That's kind of what I was afraid of. Thanks for all your help, by the way; I see you've replied to a number of threads I've started with helpful comments.

It looks like I'll need to define both walking and sprinting speeds for each creature, individually. Not an ideal situation. Still, I can probably come up with some kind of general rule to be used as a sort of rule of thumb when designing new creatures.

I think what I'll need to do is create a size chart with all the different size categories, sort different animals into each category, then compare the speeds of animals in the same category. From that, I might be able to get an idea for what "default" walking and sprinting speeds look like, based on size. Otherwise, I might have to make it completely arbitrary. If the speeds have to be personalized for each creature anyway, an arbitrary standard would probably work just as well as some complicated "default" speed based on correlating real life speeds.

For example, an arbitrary standard might say that default walking speed is 8 * your size (humans occupy a 1-yard square, hence 8 yard speed), and a sprint action is up to 5 * your walk speed, allowing you to cover a total of 6 * walk speed with walk + sprint. It's as good a place as any to start, and it gives a baseline for determining how "balanced" a creature or race might be, e.g. how much XP you might have to spend to play as that type of creature.

I'd like to find a balance between humans and animals for any default values. Most games use humans as a baseline, but this doesn't seem like a great idea in games where you might be dealing with a lot of animals or animal-like monsters (dragons, chimeras, unicorns, krakens, etc.). Once I define humans, specifically, I can then use them as a template for other humanoid creatures like elves, dwarves, goblins, etc. I'll probably want to do an entire Monster Manual-esque doc, separate from the main rules, that deals specifically with rules for creating new types of creatures and defines a whole bunch of creatures for you to use, with the main rules only having a few (like humans).

[Squire Doodad]

That's kind of what I was afraid of. Thanks for all your help, by the way; I see you've replied to a number of threads I've started with helpful comments.

It looks like I'll need to define both walking and sprinting speeds for each creature, individually. Not an ideal situation. Still, I can probably come up with some kind of general rule to be used as a sort of rule of thumb when designing new creatures.

I think what I'll need to do is create a size chart with all the different size categories, sort different animals into each category, then compare the speeds of animals in the same category. From that, I might be able to get an idea for what "default" walking and sprinting speeds look like, based on size. Otherwise, I might have to make it completely arbitrary. If the speeds have to be personalized for each creature anyway, an arbitrary standard would probably work just as well as some complicated "default" speed based on correlating real life speeds.

For example, an arbitrary standard might say that default walking speed is 8 * your size (humans occupy a 1-yard square, hence 8 yard speed), and a sprint action is up to 5 * your walk speed, allowing you to cover a total of 6 * walk speed with walk + sprint. It's as good a place as any to start, and it gives a baseline for determining how "balanced" a creature or race might be, e.g. how much XP you might have to spend to play as that type of creature.

I'd like to find a balance between humans and animals for any default values. Most games use humans as a baseline, but this doesn't seem like a great idea in games where you might be dealing with a lot of animals or animal-like monsters (dragons, chimeras, unicorns, krakens, etc.). Once I define humans, specifically, I can then use them as a template for other humanoid creatures like elves, dwarves, goblins, etc. I'll probably want to do an entire Monster Manual-esque doc, separate from the main rules, that deals specifically with rules for creating new types of creatures and defines a whole bunch of creatures for you to use, with the main rules only having a few (like humans).

Someone once told me that game design is about two things: general rules, and making as many exceptions as possible.

Having a default point to work off of is great, but ultimately lots and lots of creatures need specific setups for them in particular. You might want to try organizing speeds by physiology more than size.