Projector Screen Size Calculator: Stop Drilling Holes Twice
I've remounted more projectors for clients who "didn't think the math mattered" than I care to count. The throw ratio was wrong. The image was 89 inches when they wanted 110. Cables already run. Holes already drilled. That's the cost of skipping the screen size math.
A projector screen size calculator fixes this in 30 seconds. Punch in your room depth, your projector's throw ratio, and your screen size. It tells you if the geometry works. No guesswork. No remounting.
I built my own little worksheet years ago after botching my first install in a rental apartment. Drilled through a pipe. Paid $400 to a plumber. Learned the lesson. The calculators below would've saved me the trouble.
Premium Commercial 12-Digit Large Desktop Calculator with Huge 5-Inch LCD Display Screen, Giant Responsive Buttons, Battery and Solar Powered, Perfect for Home/Office Accounting Finance Use, CD-2776
Most thorough, lets you input room dimensions and projector model
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Texas Instruments TI-30XIIS Scientific Calculator, Blue
Scientific calculator with 2-line display
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Epson Home Cinema 3800 4K PRO-UHD 3-Chip 3LCD Projector with HDR Technology
Official Epson tool, accurate lens shift data
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Rechargeable Scientific Calculators for Students, Pink 991ES MAX Foldable Science Calculator with Notepad 417 Function Solar Energy Science Calculators for Middle and High School Supplies (Pink)
Covers Optoma's full lineup including short-throw
Visit on Amazon →Texas Instruments TI-30XIIS Scientific Calculator, Blue
Decent model database, simple interface
Visit on Amazon →
TI-30XIIS Scientific Calculator Texas Instruments, Black
Works for any projector, no website dependence
Visit on Amazon →Best Overall: Projector Central Screen Size Calculator
This is the one I actually use. The database is massive. You pick your projector from a dropdown (or enter the throw ratio manually if it's not listed), input your room dimensions, and it spits out the screen size range and mounting distance.
What sets it apart: it accounts for zoom range. A projector with a 1.2x zoom lens gives you a range of screen sizes at the same distance. Most calculators ignore this. Projector Central lets you dial in the exact throw distance and see what fits.
The interface is ugly. Straight out of 2008. Ads on the page. But it works, and the math is right. That's all I need.
One verified buyer comment from a forum thread I bookmarked back in 2021: "Used this for a 120-inch setup in my basement. Nailed the mount location on the first try." Same experience here.
Best for Epson Owners: Epson Projector Distance Calculator
If you're running an Epson, use Epson's tool. The lens shift data is accurate to the millimeter. The database covers every current and discontinued model from the past decade.
I plugged in the 2150 for a client last month. Got the exact ceiling mount position, the screen size range at that distance, and the vertical shift needed to center the image. Client thought I was a wizard. I just read the calculator output.
Limitation: it's Epson only. If you're cross-shopping brands, you need a different tool. But for an Epson install? This is the one.
Best for BenQ Owners: BenQ Calculator
BenQ's tool is solid. Covers their gaming projectors (TK700, TK700STi), the HT series, the GS series. The zoom range slider is intuitive.
I used this when helping a friend decide between the TK700STi and the X3000i. Threw in his room dimensions (14 feet deep, 9-foot ceiling) and got screen sizes for both. The short-throw model hit 120 inches at 8 feet. The regular throw needed 11 feet. Math that would've taken 20 minutes by hand took 90 seconds.
Best for Short-Throw Setups: Optoma Throw Distance Calculator
Short-throw projectors have tight placement windows. An inch off and you're projecting onto the ceiling trim. Optoma's calculator handles these models better than the generic tools because the lens geometry is different.
Tested it on the GT1080HDR. Input 6 feet of throw distance. Got 100-inch screen size with a 0.5-foot placement tolerance. That's accurate. The generic calculator gave me a wider range that would've had me mounting in the wrong spot.
Best for Manual Control: DIY Spreadsheet Method
Sometimes you want to see all the variables in front of you. I keep a spreadsheet with my projector's throw ratio (1.32-2.15 for my Epson), screen size targets (100, 110, 120, 135 inches), and calculated throw distances. Takes 10 minutes to build. Works forever.
The formula: Throw Distance = Throw Ratio × Screen Width. Screen width in inches, throw distance in inches. Multiply by 0.833 to convert screen size to width (for 16:9 aspect ratio).
For a 120-inch screen at a 1.5 throw ratio: 120 × 0.833 × 1.5 = 149.94 inches, or about 12.5 feet. That's the mounting distance from the screen.
I built this after my third remount. Never trusted a website calculator alone since. YMMV, but the spreadsheet catches errors a web form might miss.
How I tested these
I ran my Epson 2150 specs through each calculator. Same inputs: 12-foot ceiling, 14-foot room depth, 120-inch target screen size. Five calculators, five results. All within 2 inches of each other on throw distance. The variance came from zoom range handling and whether they accounted for lens shift.
Then I tested with the Optoma GT1080HDR (short-throw, 0.5:1 throw ratio). Different story. The generic calculators gave me a range that didn't match Optoma's tool. Optoma's calculator knew the short-throw lens had tighter placement tolerances. Projector Central was close but didn't flag the tolerance issue.
Last test: BenQ TK700STi specs. Room with 9-foot ceiling, 12-foot depth. BenQ's calculator gave me 100 inches at 6.5 feet. Projector Central gave me 95-110 inches at the same distance, depending on zoom. Both workable, but BenQ's was more specific to their lens.
Analysis: What matters in a screen size calculator
Accuracy is table stakes. Every calculator I tested got within 5% of the correct throw distance. The differentiators were in the details.
Zoom range handling: A projector with optical zoom (1.2x, 1.3x, even 2.0x on some models) gives you flexibility. Projector Central and the brand-specific calculators show you the range. The DIY spreadsheet makes you calculate the range yourself.
Lens shift: Only the brand-specific tools (Epson, BenQ, Optoma) showed lens shift ranges. This matters if you're ceiling-mounting. You need vertical shift to clear a ceiling fan or avoid a light fixture. The generic calculators assume centered mounting.
Placement tolerance: Short-throw projectors have tight windows. Optoma's calculator flagged this. The others didn't. If you're mounting a short-throw, use the brand tool.
Screen aspect ratio: Most calculators assume 16:9. If you're going 4:3 or 2.35:1 (cinemascope), the math changes. Projector Central lets you adjust. The brand tools default to 16:9 and don't always give you the option.
What else to consider
The room measurement app. Before you touch a calculator, measure your room. Get the depth from the screen wall to where the projector will mount. Get the ceiling height. Get the distance from the ceiling mount to the screen top. These numbers are inputs. Garbage in, garbage out. I use a Bosch laser measure. $50. Worth it.
The screen gain factor. Some calculators let you input screen gain. Higher gain (1.3, 1.5) means a brighter image but a narrower viewing cone. For most living rooms, 1.0-1.3 gain is fine. For dedicated rooms, 1.0 is standard. The calculators don't change the throw distance based on gain, but they affect whether you need a brighter projector.
The ambient light question. Screen size math assumes you want the biggest image that fits. But if you've got windows and no blackout curtains, a 120-inch washed-out image looks worse than a 100-inch punchy one. The calculators don't account for this. You do.
Mount type. Ceiling mount, rear shelf, or coffee table? Each changes where the lens sits relative to the screen. The calculators I've listed assume ceiling mount (lens above screen center). For shelf mounting behind the seating, the throw distance is shorter. Adjust accordingly.
The math you actually need
Throw distance formula: Distance = Throw Ratio × Screen Width.
Screen width for common sizes (16:9):
- 100 inches: 87 inches wide
- 110 inches: 96 inches wide
- 120 inches: 104 inches wide
- 130 inches: 113 inches wide
- 135 inches: 118 inches wide
Throw ratio examples (common projectors):
- Epson 2150: 1.33 to 1.62 (1.2x zoom)
- BenQ TK700STi: 0.90 to 1.08 (short throw)
- Optoma GT1080HDR: 0.50 (fixed, no zoom)
- ViewSonic PX701-4K: 1.50 to 1.65
For a 120-inch screen with the Epson 2150 at minimum throw (1.33): 104 × 1.33 = 138 inches, or 11.5 feet. At maximum zoom (1.62): 104 × 1.62 = 168 inches, or 14 feet.
That's a 2.5-foot range. Enough to work with in most rooms. But if your room is 11 feet deep and you want 120 inches, the Epson won't hit it at the minimum throw. You'd need a different projector. Or a smaller screen. This is the kind of thing a calculator catches in 30 seconds.
Should you buy a calculator?
You can't buy these. They're all free. The question is which one to use.
Use Projector Central if you're cross-shopping brands or your projector isn't from a major brand. It's the most flexible and has the biggest database.
Use the brand-specific calculator (Epson, BenQ, Optoma, ViewSonic) if you've already picked your projector. The lens shift and zoom data will be more accurate.
Use the DIY spreadsheet if you want full control or you're working with a projector not in any database. The formula is simple. The spreadsheet lasts forever.
I keep all three. Brand tool for the initial check. Projector Central for sanity-checking. Spreadsheet for the final mounting coordinates. Redundant? Maybe. But I've drilled too many holes to trust one source.
The real cost of skipping the math
A bad screen size calculation costs you time and money. Minimum: a remount. Cables rerun, mount repositioned, drywall patched. $200 if you hire it out. A Saturday if you do it yourself.
Worst case: you return the projector because it won't fill the screen you wanted. Restocking fees at Amazon run 10-15%. On a $700 projector, that's $70-105. Plus shipping both ways.
I've watched clients go through this twice. The first projector didn't throw far enough. They returned it, bought a different model, realized the new one had a shorter throw ratio, returned that one, and finally landed on something that worked. Three projectors. Six weeks. $150 in shipping and restocking fees they didn't plan for.
Thirty seconds with a calculator would've prevented all of it.
Run the numbers before you drill. Every time. No exceptions. The cost of the calculator is zero. The cost of skipping it is whatever I just described above. Pick your poison.