There is a calculator and it is handy . . . but the simple solution that will make you sleep well at night is this. Buy the
TF100 test kit with the
SpeedStir (it is in the options - you will be glad you did). While you are waiting for it to arrive, buy bleach, lots of bleach (be sure to check the date code). You want fresh bleach, it degrades over time and faster if stored outside, so beware of Home Depot or Lowes bleach which at least here in Texas is stored outside in the heat, some sunlight, etc. these things degrade bleach really fast. Avoid "bargain bleach" like the stuff you get at the Dollar Store, but don't waste your money on Name Brand either - store brands are generally the same, it is the date code you care about most and if there is "concentrated" that means higher % bleach but avoid fragranced and "splashes" at all cost.
Now, since you are waiting for UPS to deliver your test kit, see if you can get a local pool store to do a CYA test, and then using the instructions you were provided in the other links, SLAM your pool and do not be stingy with the liquid bleach - I learned the hard way, when it comes to pool chemicals, penny wise = pound foolish. But, I also learned that the TFP method is about 40% of the cost of what I was doing. It just takes a leap of faith to get there.
Hopefully your kit arrives within a few days, and you can start testing yourself for more accurate results. While using the local store, simply smile and nod when they tell you what chemicals to use, claim you have them if you need an excuse, but do not follow their advice. Do the SLAM per the instructions on this site. Do not give up, and do not stop when the pool "looks" good. Yes, I did that, I was still thinking about saving pennies. Had to SLAM twice but I did learn a lesson. Your pool is clear when the test kit says your pool is clear and not before.
Once clear and balanced and you like the look of your pool again - you will like it - I strongly suggest getting the instructions here and adding Borax to the pool. This is another spot where you just have to bite the bullet and buy the stuff, but next year, you will see the results paying dividends.