The short answer
Throw distance equals the throw ratio multiplied by the image width, so a 1.5:1 lens filling a 10-foot-wide screen sits about 15 feet back, while a 0.8:1 short throw lens needs only about 8 feet. Standard lenses run about 1.4-2.0:1, short throw about 0.4-1.0:1, and ultra short throw under 0.4:1. RentOurProjectors.com matches the lens to the space you have, whether the projector sits on a table, a cart, or behind a rear projection screen.
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What is throw ratio, and how do I calculate throw distance?
Throw ratio describes how far a projector must be from the screen to create an image of a given width. The formula is throw ratio = throw distance divided by image width. Rearranged, throw distance = throw ratio times image width, and image width = throw distance divided by throw ratio. Throw distance is generally measured from the front of the lens to the screen surface.
Worked example one: you want a 12-foot-wide image and the projector has a 1.5:1 lens. 1.5 times 12 is 18, so the lens needs to be about 18 feet from the screen. Worked example two: the only table for the projector is 20 feet from the screen and the lens is 1.6:1. 20 divided by 1.6 is 12.5, so the image will be about 12.5 feet wide.
How far back does each lens type sit?
The table multiplies common image widths by a representative throw ratio for each lens type. Real projectors often have a zoom range rather than a single fixed ratio, so treat these as typical positions. A standard zoom lens rated 1.4-2.0:1, for example, can fill a 10-foot-wide screen from anywhere between about 14 and 20 feet.
| Image width | Standard lens (1.5:1) | Short throw (0.8:1) | Ultra short throw (0.3:1) |
|---|---|---|---|
| 6 ft | 9 ft | 4.8 ft | 1.8 ft |
| 8 ft | 12 ft | 6.4 ft | 2.4 ft |
| 10 ft | 15 ft | 8 ft | 3 ft |
| 13.3 ft (7.5 x 13 screen) | 20 ft | 10.6 ft | Uncommon at this size |
| 16 ft (9 x 16 screen) | 24 ft | 12.8 ft | Uncommon at this size |
When should I use a short throw or ultra short throw projector?
Short throw projectors make sense when the space between the screen and the audience is tight, or when you want presenters to walk near the screen without casting shadows. They are common in classrooms, small meeting rooms, trade show booths, and rear projection setups where the depth behind the screen is limited.
Ultra short throw projectors sit only inches to a few feet from the screen, often directly below it. They work best for smaller images and need a very flat screen surface, because any wrinkle or wave in the screen is exaggerated at that steep angle. For large event screens, a standard or short throw lens on a high-brightness projector is usually the better fit.
- Standard throw (about 1.4-2.0:1): projector at the back of the seating or on a center aisle cart.
- Short throw (about 0.4-1.0:1): projector in front of the first row or behind a rear screen with limited depth.
- Ultra short throw (under 0.4:1): projector right at the screen for small images and tight spaces.
- Large-venue projectors may offer interchangeable lenses, so the lens can be chosen for the room.
Lens shift vs keystone: how do I square up the image?
Projectors rarely sit exactly centered on the screen. Lens shift moves the image up, down, left, or right optically, without changing the pixels, so the picture stays sharp and uses the full resolution. It is the preferred way to line up an image when the projector is off center or raised on a stand.
Keystone correction reshapes the image digitally to fix the trapezoid shape you get when the projector is tilted. Small amounts are fine, but heavy keystone correction uses fewer of the projector's pixels, which can soften text and slightly reduce brightness. Whenever possible, position the projector so the lens is close to the screen's center line and use lens shift for the rest.
How much depth does rear projection need?
In rear projection, the projector sits behind a translucent screen and shines through it toward the audience. Presenters can stand in front without shadows and the projector stays out of sight, which is why rear setups are popular for keynotes and stage productions. The tradeoff is space: you need enough depth behind the screen for the full throw distance.
Depth depends on the lens. A 10-foot-wide image needs about 15 feet behind the screen with a 1.5:1 lens, or about 8 feet with a 0.8:1 short throw lens. Rear setups commonly require roughly 8-15 feet, plus working room around the projector for cabling and access. Because the image passes through the screen, rear projection content also needs to be flipped horizontally in the projector's menu so it reads correctly from the front.
What placement details should I include in a quote request?
With a few measurements we can confirm which lens fits before anything arrives. A quick photo of the room from the back, if you have one, also helps.
- Where the projector can sit (back table, center aisle, ceiling, behind the screen) and its distance to the screen.
- The image width you want, or the screen size you already have.
- For rear projection, the open depth available behind the screen.
- Whether the projector must be off to one side, raised, or hidden.
- Power outlet locations near the projector position.
Frequently asked questions
What does a throw ratio of 1.5:1 mean?
It means the projector must be 1.5 feet from the screen for every 1 foot of image width. For a 10-foot-wide image, that is about 15 feet.
Can I make the image bigger by moving the projector back?
Yes. Moving the projector farther away increases the image width in proportion to the throw ratio. A larger image also spreads the light over more area, so it will look somewhat dimmer.
Does a short throw projector cost me brightness?
Throw ratio and brightness are separate specs. A short throw projector puts the same rated light on a screen from a closer position; the image width and room light still determine how bright it looks.
Can a projector be mounted on the ceiling for an event?
In some venues, yes, using existing mounts or rigging, and the image is flipped in the projector's menu. For most temporary events, a projector stand or cart at the right throw distance is simpler.