Tama madami ang online calculator check ng viewing distance and screen size para makuha agad ang size ng screen na puwede sa room size pero as for me i just need to check ano maganda na viewing size according to my my eyes mahirap naman kaya ng 120 inch sa room ko kung in the long run masakit din sa mata ko. Saka i need to consider din my family's viewing kung ok sa kanila ang ganung size and viewing distance. Kaya PJ muna ako kesa sa sabay sila kahit na alam ko na kaya ng wall and viewing distance. 
Huh?
From the start constant na agad yung viewing distance unless your room is so big that you can play with distance. Pero ganoon pa man, yung recommended screen size will be dependent on your viewing distance which is dependent naman where you will place your seaT.I'm sure alam mo naman seating arrangement mo? As for screen size, it is always advisable to get the maximum screen size you can depending on viewing distance. Although a smaller screen can be nicer to look at ESP if low lumens yung pj mo, but yung bigger screen naman is always the target kaya you choose to go the pj way.
Ngayon if you really want to actually look at size then another option is to put masking tape on wall corresponding to your estimated screen size that is dependent on viewing distance. Target here is minimize eye panning from left to right just to view the whole screen. Better if around 10" from both sides Lang ng screen ang mawala sa vision mo.
But hey it's your decision naman so it's your call. Ang point ko Lang is may purpose yan screen calculator kaya andyan yan
now if consider mo is model option then that's another problem,like if you want it fixed or retractable? If you want to have an extra monitor or not? Yan ang iniisip maige
