The Hell Knight in Doom 3 is generally described as about 10 feet tall (around 3 meters) and is the largest non-boss enemy in the game.

Quick Scoop

It’s also portrayed as huge, very muscular, and heavy , with a massive skeleton and a towering frame that makes it stand well above the player character.

In plain terms

  • Approximate height: about 10 feet / 3 meters.
  • Build: massive, muscular, and bulky.
  • Role: the biggest non-boss enemy in Doom 3.

If you want, I can also compare its size to the Doom 3 marine or to other Doom demons.