Too many people order a projector screen only to find out that they blew it, and have to return it, because they didn't carefully determine the size screen that is best for them. Typically those needing to return a screen find they have to pay significant restocking fees. The most common cause seems to be not anticipating the the entire size of the screen, with its trim or borders.
If you are getting a basic fixed wall screen (permanent on your wall), and the projector screen has a basic black border, figure that the border or frame is 1.5 to 2" all the way around. So if you want a 100" diagonal screen (87" wide) for actual mounting you will have 87" + 3 or 4 inches total width. (And also 3 to 4 inches to the total height of the screen).
However, if you, like most projection screen buyers, want a really nice trim (typically some sort of velvet like, soft, light absorbing material, usually with nice bevelled edges), those frames, typically, are 3 to 5 inches wide. So again, if you need a 100" diagonal screen, you'll have 87" of screen width plus the frame with add 6" (but more typically) 10 inches to the width, so you would need 93 to 95 inches of mounting width for your projection screen.
Of course, that also means the same extra amount to the total screen height - 55.5 - 59.5 of total height.) Note, some fixed wall screens have as much as 6 inches all around.
Click here, for how to calculate the dimensions of a projector screen's surface area.
When you speak with your dealer about the screen, be sure, if you have limited space, that the border/frame is calculated into your mounting requirements.
Basically there are two types of pull down projection screens - standard and tensioned screens.
The first thing to realize, is that the housing for the screen will be wider than the screen surface. This amount can be as little as 3" wider on each side of the screen, but more typically 5" or more per side. Typically, with pull down projector screens, the screen surface is centered relative to the projector screen housing. Again, if you have a tight area and are trying to put in the largest possible screen, be sure to ask your projector sales consultant what the width of the case is - how much wider than the screen surface. The good news, just about every screen manufacturer publishes the outer dimensions of the screen as well as the screen surface dimensions.
The typical pull down screen will have a 2" black border on the left and right, plus the extra, width of the casing. All considered, figure the projector screen's case width will be 6" - 12" inches wider than the projection surface's width.
In order to keep the screen surface as close to perfectly flat, most projector screen manufacturers (Stewart Filmscreen, Da-lite, Draper, Vutec, Elite, Screen Innovations, etc.) offer versions of their screens with tension. There is nothing more distracting (other than lots of ambient light) than a screen that isn't perfectly flat (the advantage of fixed wall screens). If your screen isn't completely flat, then you will notice a rising and falling of the portion of the image hitting the non-flat areas, when watching a scene that is panning from side to side. Tensioning, normally consists of a border on the sides that flares out to the bottom of the screen (see the image). In the example shown here, this is my 128" diagonal Stewart Filmscreen Firehawk.
Tensioned screens are highly recommended, especially on the larger screens. Say 110" diagonal or greater, however, if budget allows (tensioning significantly adds to the cost), it is recommended for all pull-down (and motorized) projection screens. Over time, projector screens without tensioning are likely, when opened, to have areas that are no longer flat, so you might find yourself needing to replace a non-tensioned screen after a couple of years, or so.
The amount of extra width for a tensioned screen will vary, but for something in the 100" diagonal range, expect the tensioned border to be around 6 inches on each side. Then figure the case has to accomodate that, so expect the case to be 14" to 20" wider than the projection surface. Now that is a lot of extra width to account for if you are trying to use the largest screen possible!
There is also the height issue, for the case and the "drop". For more information, scroll down below the Motorized Screen paragraphs.
Unlike pull-down and fixed wall projector screens, not all motorized projection screens are "centered". You will find some extend much more to one side than the other, relative to the screen surface. While this is the exception there are plenty of screens like this. Often this is because some projector screen manufacturers, put the motor, and a lot of the control/power mechanism inside one side of the casing. (An example of this are some of the Da-lite Advantage models.)
As a result, you might have a 100" diagonal motorized screen, (87" wide screen surface), with a case that extends more than a foot on one side, while significantly less on the other side. You need to figure this into your mounting solution.
Generally, a motorized screen housing will be wider than a pull-down, for the same size screen. In the case of my motorized 128" Stewart Filmscreen Firehawk (a good example), which is tensioned, I've got 6.5" of border on each side of the surface, and approximately 3 inches of extra case on each side. The end result. My screen surface is roughly 112" wide, but the case is 130" wide - an extra foot and a half!
When you mount your pull-down or motorized screen (including motorized screens housed inside your ceiling), you need to determine where the top of your screen surface will be, to properly mount and position your home theater projector.
Most screens come standard with a 6" drop. The drop is the black cloth, vinyl, or other material used. In other words when you pull down your manual screen, or "drop" your motorized screen, the top of the projection surface will not be flush with the case, but normally about 6 inches lower. Add to this, the height of the case, and you have a significant amount of space needed between the ceiling and the top of the projected area.
A typical case (depending on whether motorized or manual) will be 3 to 8 inches in height. (Motorized will probably start at 4 inches.
Let's assume the case is 5" high, and you have 6 inches of drop. If you mount the projector screen flush with the ceiling, you are 11 inches down to the top of the projection surface.
Why is this a big deal? It may not be, but let's assume for a moment that you have an 8 foot ceiling, and want a 110" diagonal screen.
The screen surface will be 54.5" high. Add to that a typical 11" of case and drop. (assuming you can mount flush with the ceiling), and you have 63.5" to the bottom of the projection surface. Take your 8 foot ceiling (96") and subtract the 63.5" and you have the bottom of your projection screen's surface only 32.5 inches off the floor (about mid-chest level when sitting). You now have to consider if that is practical, (especially if some people will be sitting behind others). That's one reason those dropping the really big bucks on a home theater, often buy fancy home theater seating, and use risers so that the back seats are higher, allowing the people in the back, to see over those in front.
In my own home theater, I have seating front and back, but no risers, so I mounted my screen so that the bottom of the projector screen surface is almost 52" off the floor. That puts eye-level below the bottom of the screen - which many will dissaprove of. Since my seating reclines, it works just fine for us.).
One important point about the drop. Most manufacturers will allow you to order a custom amount of drop on motorized projection screens, and in some cases on pull-down projection screens. In my situation, due to the location of window casings, my screen had to be mounted at an exact height. As a result, I ordered my screen with 17" of drop, to get the screen surface where I wanted it.
Normally the cost of custom length drops is pretty minor, however, expect to wait an extra week or two for a custom drop. Also allow extra time if you are ordering a custom size - my 128" Stewartfilm Firehawk is also a non-standard size, but I knew exactly what I wanted, as I was replacing a larger 140" diagonal screen.
Some of the major projector screen manufacturers that have been making quality screens for businesses for decades, require dealers to actually sign off on a screen engineering drawing just to start the order process. StewartFilm comes to mind, requiring them. Da-lite offers drawings but I'm not sure they require signoff. At least one dealer I work with sends faxes or emails pdf's of the drawing, to the customer. The drawings show all critical dimensions to customers. The dealer has the customer to sign off on the drawing, and then places the final order.
Signing off is very typical for commercial installations, so why not take advantage of these drawings for your home screen, to make sure your screen fits! Since these drawings are available from the projection screen manufacturers that sell most of the screens in the U.S., I recommend you ask your authorized dealer for a drawing with dimensions, before you place your order. If you sign off, and they botch the screen, you've got your copy showing exactly what you were expecting! That protects you.
Note, not every manufacturer offers this service, but all of them publish the full specs of a screen. A typical screen price catalog that dealers use, will list the "outer dimensions" of screens as well as the surface area. From other manufacturers they may have a "standard" drawing, your dealer can send you.
Bottom line, even forgetting restocking fees, and the cost shipping back a projector screen that doesn't work for you, you just don't need the aggravation! So:
Remember, screens are an integral part of the performance of your home theater (or home entertainment) system. It makes little sense to spend $200 for a projection screen for a $5000 home theater projector, than it does to spend $2500 on a screen for a $999 projector.