For people, there's a recommended weight range based on height and age (and maybe some other parameters) and I assume cats have a similar guidelines and I feel my cat may be too heavy. As there are many breeds of cats with different ideal weights based on their general size, is there any way to generally assess if a cat is at an ideal weight based on other information?
If you want to know whether your cat is over- or underweight, the most reliable way to know is to take the cat to a vet. My vet can tell just by looking, even if she doesn't know the exact breed of cat.
Barring that, it's better to look at body composition than actual weight measurement if we're going to talk in generalities. As people mentioned in the comments, different breeds have different weight ranges that can be considered healthy (anywhere from 5 pounds on the low end for breeds like Siamese to around 20ish pounds for Maine coons).
Here are some tips that you can use to tell generally whether a cat is a healthy weight:
- Defined waist. You can tell this by both sight and feel: when looking at your cat from above (when the cat is standing), you should see a visible waist at the bottom of her ribs. In your case, where you said the long hair gets in the way of visual indicators, use your hands. Rub your hand along the side of the cat from ribs to hips; at the bottom of the ribs, there should be an indentation. If your cat's side feels like a straight line - or bulging outward past its last rib - your cat is overweight.
- Very little evidence of a belly pouch. If your cat has a flabby pouch of skin and fat that hangs lower than the ribs on the underside of its belly, then it's probably overweight. There should be some fat there (a cat with a deep tuck on its underside where the ribs end is underweight), but if it hangs lower than the ribs or wobbles from side to side a lot as your cat moves, your cat might be overweight.
- Ribs can be felt. You should be able to feel individual ribs on your cat when petting him or her. If you can see the outlines of ribs, your cat is probably underweight, but if you can't feel them at all, there's probably an unhealthy layer of fat covering them.
- Face isn't too round. If you have a long-haired cat, you'll need to kind of smush down the fur on the face to tell this one, but basically, if your cat has really chubby cheeks, chances are pretty good she's carrying extra weight elsewhere on her body (though cat face shapes vary a lot as well, so don't use round cheeks as a sole indicator of excess weight).
If you think your cat is obese, talk to a vet before implementing any sort of dieting program. Your vet can tell you for sure whether your cat is overweight or obese, as well as inform you of any health problems your cat currently has that might be related to an unhealthy weight. It's very important not to put cats on crash diets because if they lose weight too quickly, they can actually wind up with more health problems (and any pre-existing medical problems can be exacerbated).