He's about a meter tall (roughly 3ft) in anthro and humanoid forms and just under 60cm/2ft in Fox form. Because I like keeping the same mass as a fox and as an anthro/humanoid, and realism ftw. As for my "shadow" sona, he has no definite size. Because he isn't quite physical anymore.
I don't use my fursona but the anthro version of him s just over over 3 feet. I wanted him to seem like his actual species so I used the average length as his height. Actually, he's shorter than the average (4 to 5 feet) which fits since I'm shorter than average.
When my sona stands on his hind legs he comes up to 5'4" He travels quadruped style sometimes too which makes him appear smaller.
His other size is his little chibi cartoon form and he's about the size of a hamster. This is not an actual size for him, I just draw him that way like anime artists do with their characters sometimes.
FTC is the same height, age and weight as me.
When i change i will change him (i.e if i turn chubby or old he will get wrinkles or fatter.) I feel like I'm more deceiving or lying to others if i don't.