I see the units as ~1m with some wiggle room, mostly matching Minecraft. All your animals are single-tile entities only when selecting them as they also overlap and don't exclude other animals from sitting on the same tile. So some of them being 2 tiles long is if anything, more logical than enabling like 6 of them to overlap each other as they're clamoring to get outta the Coop and eat that tasty Grass.
The Horse is particularly funny as it's more than 1 tile wide when going North and South, needing a 2-tile gap to fit your BigButtHoss through. Yet it can apparently shimmy through a single tile East-West space. Maybe tiles are all buttered on their N and S faces but not E and W purely for the exclusive reason to squeeze your Horse thru. Now I'm wondering how to imagine the in-game lore for that.
Of course when it gets to buildings, all measurements are right out.
Except if all buildings are TARDISes.
Ye-e-e-e-es that's it, they're all dimensionally transcendental. Problem super solved now, NEXT!