UPDATE: This post is somewhat obsolete given how much more detailed the Size rules are in SWADE.

I struggle all the time with understanding Size in Savage Worlds, so to help myself I compiled an ascending list of Sizes and what creatures from various books are listed as being at that Size.

For every 2 points Size difference, it’s +1 to be hit and -1 to hit. Creatures from Size +4 to +7 have the Large ability and fill a 2” square on the tabletop. From Size +8 to +10, they are Huge and occupy an area 3” square. If the creature is +11 or more, it is considered Gargantuan and occupies a 4” square area. I would expect a Colossal creature to essentially take up a Large Burst Blast Template.

 -2: Tiny, rat-sized (SWDE), Sprite (UFG)
 -1: Small, big housecat, small dog, up to Halfling (UFG)
  0: Human-sized
 +1: Slightly larger than human, i.e. orc (SWDE), Cyborg (SFoNA), Collector (FC)
 +2: Significantly larger than human, i.e. Brodkil, Lesser Demons (SFoNA)
 +3: Big, Splugorth Minion Barge, Ostrosaurus, Gargoyle (SFoNA)
 +4: Large, Great White Shark (SWDE), Fury Beetle (SFoNA)
 +5: Large, Drake, Hammer Beast, Feculence Daemonix (SFoNA)
 +6: Large, Dragon Hatchling, Immolator, Rhino-Buffalo, Greater Demon (SFoNA)
 +7: Largest of the Large, Wooly Worm (SBBoFF), T-Rex, Lloigor, Dagon (RoC)
 +8: Huge, Hunting Horror, Shoggoth (RoC), Sirean (SBBoFF), Adult Dragon (SFoNA)
 +9: Huge, Star Spawn of Cthulhu (RoC), Fire Dragon (SWoFG)
+10: Hugest of the Huge, Giant Worm (SWDE), Demonic Titan (ETU)
+11: Gargantuan, Tree Man (FC), Maze Dragon (DLR)
+12: Gargantuan, Gigantic Raging Monster (SFoNA), Sea Serpent (FC)
+13: Gargantuan, Cave Dragon (SWoFG)
+14: Gargantuan, Submosaur (SWoFG)
+15: Most Gargantuan of the Gargantuan, Rattler (DLR)
+16: Colossal, Giant Monster (SPC)

  SWDE: Savage Worlds Deluxe Edition (the core rulebook)
 SFoNA: Savage Foes of North America (from Rifts for Savage Worlds)
   RoC: Realms of Cthulhu
   ETU: East Texas University
   DLR: Deadlands Reloaded
   SPC: Super Powers Companion
    FC: Fantasy Companion
 SWoFG: Savage World of Flash Gordon
   UFG: Ultimate Fae Guide
SBBoFF: Savage Bestiary: Book of Fantasy Fiends