The other person is almost upright sitting inside it with space to spare, so for an average human being conservatively being 1.7 m, that means there is around a meter of space inside the thing. Add on the bottom part and the top part, and that's how I came to the conclusion that it must be 1.5 m.
The other person seems to be both in front of and behind the dishwasher, as she has a larger body than the girl inside the dishwasher, but she is also standing behind it. So I guess perspective is completely off.
That said, it's a cartoon, so there's no point in trying to measure things. I just thought that I would not ever be able to sit up inside a dishwasher, not by far. Maybe a kid could?