Your already there...and the info has already been provided.
No confusion or mistakes if you follow the given advice.
However.......................here is the location most use: http://www.projectorcentral.com/projection-calculator-pro.cfm
Be advised that if you do not use it (...or read it....) correctly it can actually steer you wrong.
As for my advice, I don't usually make comment as to why Noobs should take my suggestions and run with them out of hand. But truthfully, I have many years experience doing installations that run the gamut of both normal and no-so-normal situations, and that encompass virtually any / every PJ of note available. I'm on here to make things as quick, as affordable, as high performing as I can for Members such as you.... and as easy a possible for both Noobs and experienced Members who are making a DIY Screen for the first time, and who desire to nail it down ...also "the first time".
Some do like to explore options...even try things that are no so "advisable" and learn through doing it themselves from the get go.
And that's cool......but we've seen some pretty bleak end results from them going down that road, and / or comments about how frustrated they become...or sore-eyed and mush-brained from hours of confusing and contradictory comments and advice.
Your situation is a simple one to accommodate, and can be made difficult only through indecision or misapplied advice.
Sooooo...............it's your call to make from here on.
Me...I'm going to go see a Early Afternoon Movie. Strictly in the name of business, don'tcha know.