Projection throw distance vs screen size

[speed33301]

Brand new to proejction and HDTV. Currently using a Thosiba 61 HD ready TV but do not have the HDTV tuner or Sat box. Buidling a new house and I am having the 4th Bedroom converted to a media room. Size of room is 12.5' X 17.5' pre-wire for DD 7.1. I have orderd an Optoma EXPro745 from tigerdirect. AFter doing some research here, I went to projectcentral and started using the distance/screen calcualtor. Now the questions.

Is the screen size you use in the calcualtor the actual viewable area? (or overall size, so I can decide where to mount the projector)
Elite VMAX100XWH 101-Inch 16:9 Electric Projection Screen Whte
Nominal Diagonal: 101" (16:9)
Viewing Size (H x W): 49" x 87"
Screen Size (H x W): 57" x 91"
Over All Size (HxWxD): 61.5" x 101.8" x 3.2"

It also mentions a screen gain of 1. What is that? Using a screen gain of 1 it states I can use the economy mode to save on bulb life. (5K hrs)

Great site, thank you for your replies.

[hch]

Speed, I'm not the ultimate authority, but I did set up my own projector system. The calculator should give you a good idea of the size of the area that will be lighted by the projector at a given distance. Whether you are viewing an image on the entire lighted area depends on aspect ratio, zoom, etc. A projector will have some lens zoom/focus adjustability to allow for perfecting a "pretty close" install. The gain of 1 on the screen means it should be basically neutral for reflecting light from the projector. A higher than 1 gain will reflect more light giving a brighter image, but usually at the cost of viewing angle. A lower than 1 gain will reflect less light but give deeper blacks and a higher constrast ratio. More or less. I use a screen with a gain of 1 and the low bulb setting. As I'm sure you know, another must for a projector setup is good ambient light control. If you have too much ambient light, the screen gain of 1 and low bulb mode may not work well. Good luck!!!