Read the label and use your slider (if you don't have a slider, figure about 50 calories per point). There's so much variation because different brands use different ingredients and different sized bags.
Figuring out the points for popcorn is DAMN CONFUSING. They give values for unpopped (how are you supposed to know what 2 tbsp unpopped yields in popped??) and popped but it never seems to come out right whenever I calculate it.
I gave up for now.
I don't remember where I read (not sure if I can even post it if I did) this but 1 tbsp is suppose to yield an average of one cup popped. I had to find this information when I began using an air popper. More popcorn for less points.
Good point Irishchik, except I found with my air popper too many unpopped kernels. So I switched to the microwave. Someone needs to make a good air popper with a trap door or something
I use a microwave popcorn popper (Presto's Orville Redenbacher model), and I measure the kernels by weighing them. The points are much less that way, and I get lots of popcorn. I can even. Use my healthy oil in the popper if I still have some left. If I don't use oil, I spray the corn w/Pam so that salt or other seasonings will stick.
If you are having a lot of unpopped kernals in your airpopper, try another brand. I got some from Walmart that was horrible. Got it from Kroger and there might be 2-3 unpopped kernals in a batch. Also, keep it in the fridge helps. If popcorn is too dry or old, it doesn't pop. Both cases I used the store brand. Kroger beat Orville Redenbacher in a previous trial I did.