I think low fat is considered 30% of calories or less from fat. So once you have established your optimum calorie intake for weight loss, then you can find out how many fat grams you can have per day.
There are a few websites, and of course books that have great nutritional information. I keep track daily and try to write everything down and plan ahead.
I am currently eating approx 1500 cals, so I limit myself to 50 fat grams or 30% of 1500 (each fat gram has approximately 10 cals...so that equals about 500 cals from fat or about 1/3 of calorie intake).
I know you can go lower, maybe about 20%, but you should never go below 10% or 1200 cals since this can be detrimental to your body and your metabolism in the long run.
Curious to see what others are doing!
Frouf