How much pasta?

You have all been there, the water is boiling, you confidently grab the bag of pasta and rip it open, then a dilemma! "Gad Zooks ..." you declare out loud, "... how much pasta should I make?". You always hate to make too much, especially when it ends up being a moldy experiment in a ziploc container a week or two later, and not enough could be equally traumatic. Think... has anyone ever taught me a trick about this, nope, have I learned anything useful from the Swedish chef, well not for this particular problem.
Now if this were rigatoni or elbows you could just measure the amount in a measuring cup, but the long spaghetti / fettucine noodles on the other hand are what pose a challenge.
I did see a solution at Sara's family cottage which was a plastic shim with various holes in it just for this purpose, including how many people each would feed. To everyone's bewilderment I found this to be ingenious. I have not been able to find this item in any store, and I have never given up the search. For now I just continue to make too much.