This is when you have to be really aware of items that are labeled "no fat" (like cooking sprays). As long as 1 serving is less than 1 gram they are legally allowed to call it "no fat".
I am not sure which brand it is but one "no fat" cooking spray lists 7 calories per serving (which is less than 1 gram), however if you look, 1 serving is 1/3 of a second.
Now, honestly, who sprays for only 1/3 of a second? Or even just 1 second for that matter. But lets just say that you spray for only 1 second. That is 3 servings times 7 calories per serving so you have just added 21 fat calories to whatever you are cooking. Do that to 3 different pans and you have added 63 fat calories. 63/9=7grams. And that is just at one meal.

The longer you spray the higher it goes.
2 seconds would be 126/9= 14 grams.

I try to keep my total fat to 30% or less.

If an item (or meal) is 300 calories, 30% would be 90 calories or 10 grams.
90calories/9calories per gram = 10grams
If an item (or meal) is 500 calories, 30% would be 150 calories or about 16.6 grams.
500/9=16.666666

If I keep each individual item at 30% or less then my total for the day will be 30% or less and I don't have to do all the adding and multiplying and dividing a whole days worth of numbers.
Most people are creatures of habit. They eat the same things over and over. I know I do. So, over time I have learned which foods are in the correct range and which are not so I don't have to do the math everytime I eat anything (I already know what the numbers are). Makes eating a lot less stressful.

If it is something new, or something I don't eat very often I do have to think about it.