The Metamorphosis question

From the way I read it, I felt like he remained around man-sized. Which honestly makes it kind of horrifying for everyone else involved.

It differs throughout the story, at one point he seems to be man sized at another he can't be much larger than an average bug.

Así como no alcanzamos a conocer su verdadero tamaño, tampoco sabemos qué tipo de animal es exactamente. Le que más atemoriza creo que es esa dualidad en la que permanece: tiene cuerpo de animal pero tiene la conciencia de humano. Vive como animal pero siente y se emociona como humano.

I agree with Gerd's comment above. My general feeling is that he starts off human size, but then gets a bit smaller over time.

Since he seemed to be just large enough to turn the doorknob, I always guessed he'd be a little bit longer than one meter.

It's generally accepted that Gregor Samsa was transformed into a human-sized "monstrous vermin"--possibly a cockroach, though it's also vaguely probable that the insect image matches that of a human-sized bedbug, which would also explain some of Gregor Samsa's shrinkage during the course of the story. He flattened, which is precisely what bedbugs do when they're starving...and human-sized bedbug...well...I'm guessing that would also explain some of the more violent character interactions. Yeah, a human-sized cockroach is enough to cause pretty strong feelings of revulsion and disgust as expressed by Gregor Samsa's family, but the heightened revulsion seems more apt to one reacting to a human-sized bedbug, and the whole shrinking/flattening/dehydrating element of Gregor Samsa's demise does seem to match bedbug-shrinkage due to starvation, and also emaciation due to tuberculosis, which killed Kafka much later in life, and could surely have played a major role in the story. TB was very common, back in the day, and tuberculosis-victim imagery co-mingled with insect ick-factor strangeness was definitely something Kafka might possibly have used to heighten the impact of the story.

It's strange because he can pass underneath the door and is heavily wounded by apples.

I had the feeling his size changed along the story. It is oniric litterature, after all.