game isn't quite on the same scale for all DGs. my interpretations based on the fluff and the in-game graphics.
Torchbearer - size of a tall human male, floats about 10 feet off the ground in fire mode
Regulus - slightly larger than a human, 7-8 foot tall and fit. would have a wing span of about 20 feet if he still had wings.
Unclean Beast - about the size of an extra large Rhinoceros or other large land mammal. he kinda looks like an inside-out cross between a gorilla and a wolf, but would stand about 10-12 feet tall at the shoulder.
Rook - fuckin gigantic. gotta be 50 feet tall or more. i tend to imagine him being about the size of a smallish apartment building (like 6-8 stories tall).
Erebus - similar size to Regulus, just slightly larger than a human. floats about 2-3 feet above the ground.
Sedna - the girl is normal human size (about 5'4" for most women) but her tiger Seela is gigantic, probably 6 foot high at the shoulders. Sedna's head is probably about 8 or 9 feet off the ground on Seela's back.
Queen of Thorns - the queen herself is a bit smaller than a human, but much larger than most faeries. going with about 5 feet tall. the beetles+flower chariot she rides is fairly large, like the size of a car or something. so imagine a girl standing up on the back seat of a convertible, about that size.
Oak - Oak used to be a normal person and all that's left now is his armor. i see 2 ways to interpret this. 1) its literally the armor the man used to wear so its man-sized. or 2) the armor has been re-forged (alluded to by Oak who often says "anvils sing, armor forged, i am reborn") and is now substantially larger than a normal human as befits his immense spiritual stature. i'd say he could easily be 10-12 feet tall re-forged as a giant suit of armor. personally i favor version 2)
