Projector Throw Distance and Screen Size Calculator
Enter your throw ratio and screen size (or throw distance) to find the perfect projector placement. Choose which value to solve for, pick your aspect ratio and unit system, then get throw distance, screen dimensions, throw ratio classification, and a recommended minimum lumen output based on your room lighting. Results update instantly as you type.
Formula
Worked example
A projector with a 1.5 throw ratio and a 120" 16:9 screen: width = 120 × (16 / sqrt(256 + 81)) = 120 × 0.8715 ≈ 104.6 inches = 8.72 ft. Throw distance = 1.5 × 8.72 = 13.1 ft. For a moderately lit room with gain 1.0, the recommended minimum is about 3,500 lumens.
What is throw ratio and why does it matter?
Throw ratio (TR) is the fundamental specification that governs where your projector must sit relative to the screen. It is defined as the throw distance (lens to screen) divided by the width of the projected image: TR = D / W. A throw ratio of 1.5 means you need 1.5 feet of distance for every 1 foot of screen width. A ratio of 0.3 means an ultra-short-throw projector only needs 0.3 feet of clearance - those models can sit just inches from the wall. Manufacturers always publish this figure in the specification sheet, and zoom lenses give a range (for example 1.3-2.0) rather than a fixed value. When choosing a projector, start with your available throw distance and the screen size you want, then use this calculator to find the throw ratio you need - that narrows the field dramatically.
How to calculate screen dimensions from a diagonal size
Screen size is always quoted as the diagonal because it is the single largest number and easiest to compare, but what you care about in practice is the width and height. Width and height depend on the aspect ratio. For a 16:9 screen, the width-to-height ratio is 16 divided by 9 = 1.778. Using the Pythagorean theorem: Width = Diagonal × (16 / sqrt(16² + 9²)) and Height = Diagonal × (9 / sqrt(16² + 9²)). For a 120-inch 16:9 screen that gives Width = 120 × 0.8715 ≈ 104.6 inches and Height ≈ 58.8 inches. The throw ratio formula always uses width, not diagonal, so this conversion step is essential - and this calculator handles it automatically for every supported aspect ratio.
How many lumens do you really need?
A projector's ANSI lumen rating is the average brightness measured across nine points on the screen. What you need depends on two things: screen area and ambient light. A dark home theater with blackout curtains can produce a beautiful image at 1,500-2,000 lumens on a 100-inch screen. The same screen in a living room with daylight pouring in may need 4,000-6,000 lumens to look acceptable. Screen gain matters too. A matte white screen (gain 1.0) scatters light in all directions; a high-gain screen (1.8-2.5) concentrates reflected light toward the center seats, making the image appear brighter from the sweet spot but dimmer at wide angles. The AVIXA DISCAS standard used by professional AV designers targets at least 16 footLamberts for a dark room and 40+ for ambient-lit environments. This calculator applies those targets to your screen area and gain to give a practical starting figure - then add 10-20% headroom because lamp brightness degrades over time.
Choosing between projector types
Ultra-short throw (UST) projectors have throw ratios below 0.4 and sit right against the wall, eliminating the long cable run and the risk of someone walking through the beam. They are popular in living rooms and for large interactive displays. Short-throw projectors (0.4-0.99) work well in smaller rooms where ceiling mounting over a long distance is impractical, and they cast fewer shadows when people move near the screen. Standard-throw projectors (1.0-2.0) are the most common and offer the widest selection of models and price points; they suit a dedicated home theater or classroom where the throw distance is set at installation. Long-throw projectors (above 2.0) are for auditoriums, large conference rooms, and venues where the projector must be far from the screen. Your room geometry is the deciding factor: measure your maximum available throw distance, decide on the screen size you want, and the required throw ratio falls out directly from this calculator.
Throw ratio classification by projector type
| Type | Throw Ratio | Typical Use Case | Screen Distance (100" 16:9) |
|---|---|---|---|
| Ultra-Short Throw (UST) | Below 0.4 | Wall-hugging, living room, interactive | 1-2 ft (30-60 cm) |
| Short Throw | 0.4 to 0.99 | Small rooms, reduced shadows | 4-8 ft (1.2-2.4 m) |
| Standard Throw | 1.0 to 2.0 | Most home theaters, classrooms | 8-15 ft (2.4-4.6 m) |
| Long Throw | Above 2.0 | Large venues, auditoriums | 15 ft+ (4.6 m+) |
Standard industry classifications for projector throw ratios. Check your projector spec sheet for the exact figure.
Frequently asked questions
What is a throw ratio?
A throw ratio is the projector's throw distance (lens to screen) divided by the screen width. A throw ratio of 1.5 means the projector must be 1.5 times the screen width away from the screen. Lower ratios let the projector sit closer; ultra-short-throw models have ratios below 0.4.
How do I find my projector's throw ratio?
Check the specification sheet or manual for your projector model. Most manufacturers list it as a single number (fixed lens) or a range like 1.3-2.0 (zoom lens). You can also find it on the manufacturer's website or in RTINGS/ProjectorCentral review databases. If you have both the throw distance and screen width already measured, enter them into the "Solve for throw ratio" mode of this calculator.
Can I use this calculator for any aspect ratio?
Yes. The calculator supports 16:9 (standard HDTV), 16:10 (common in education and business projectors), 4:3 (older XGA standard), 21:9 (ultra-wide), and 2.35:1 (CinemaScope). The throw ratio formula always uses screen width, and this calculator converts your diagonal input for each aspect ratio automatically.
Why does screen gain affect the recommended lumens?
A screen with gain above 1.0 redirects more light toward the primary viewing angle, making the image appear brighter from those seats. This means you need fewer lumens from the projector to hit the same perceived brightness. Conversely, a very low-gain or ambient-light-rejecting screen absorbs some light but cuts reflections from room lighting, which changes the equation in a different way. The calculator uses your gain value to scale the recommended lumen output accordingly.
Does the throw distance include the projector body length?
Throw distance is always measured from the projector lens, not the back of the chassis. When ceiling-mounting, measure from the lens position (typically a few inches forward of the body) to the screen surface. Manufacturers also list a "lens offset" or "lens shift" range that governs how far the image can be shifted vertically without keystone correction.
What is the difference between a short-throw and ultra-short-throw projector?
Short-throw projectors have a throw ratio of 0.4-0.99 and typically sit 2-8 feet from the screen. Ultra-short-throw (UST) projectors have ratios below 0.4 and sit just inches to about 2 feet from the screen, often on a shelf or table directly below the display area. UST models are usually more expensive and use mirror-based optics that are more sensitive to placement precision.