To calculate projector distance, multiply the projected image width by the projector’s throw ratio.
Throw distance = throw ratio × image width
Use the image width—not the screen’s diagonal. If the projector has a zoom lens, calculate a minimum and maximum distance rather than relying on one number. The result is normally measured from the projector lens to the screen surface; confirm the reference point in the projector’s installation manual before mounting.
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Projector throw-ratio calculator
Use these formulas to plan a projector, screen, classroom, home theater, office, or golf-simulator installation:
Throw ratio = throw distance ÷ image widthThrow distance = throw ratio × image widthImage width = throw distance ÷ throw ratio
For a projector specified as 1.15–1.50:1, calculate both ends of the range. The lower ratio creates the largest image from a given distance; the higher ratio creates the smallest image.
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Required inputs
- Projector throw ratio, or minimum and maximum throw ratios.
- Active image width, screen width, or screen diagonal.
- Screen aspect ratio, such as 16:9, 16:10, or 4:3.
- Units, such as inches, feet, millimeters, or meters.
For a more reliable installation plan, also account for the projector model and lens, optical zoom, chassis depth, lens shift, vertical offset, screen frame, wall position, ceiling mount, ventilation, and cable clearance.
Convert screen diagonal to image width
Throw ratio is based on image width. If you know only the diagonal, convert it first:
Image width = diagonal × aspect-ratio width ÷ √(aspect-ratio width2 + aspect-ratio height2)
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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minute| Aspect ratio | Width from diagonal |
|---|---|
| 16:9 | Diagonal × 0.8716 |
| 16:10 | Diagonal × 0.8575 |
| 4:3 | Diagonal × 0.8000 |
| 2.35:1 | Diagonal × approximately 0.9200 |
| 2.39:1 | Diagonal × approximately 0.9220 |
A 100-inch 16:9 image is approximately 87.2 inches wide. A 100-inch 4:3 image is 80 inches wide. Applying the same throw ratio directly to both diagonals would therefore produce the wrong result.
Common width conversions
| Diagonal | 16:9 width | 16:10 width | 4:3 width |
|---|---|---|---|
| 80 in | 69.7 in | 68.6 in | 64.0 in |
| 100 in | 87.2 in | 85.7 in | 80.0 in |
| 120 in | 104.6 in | 102.9 in | 96.0 in |
| 150 in | 130.7 in | 128.6 in | 120.0 in |
How far should a projector be from the screen?
- Choose the active image aspect ratio.
- Convert the screen diagonal to image width if necessary.
- Find the exact projector or lens throw-ratio specification.
- Multiply image width by the throw ratio.
- For a zoom range, calculate both endpoints.
- Add room for the projector body, mount, screen frame, cables, and adjustment range.
- Check lens shift and vertical offset in the installation documentation.
Example: 100-inch 16:9 image at 1.13:1
A 100-inch 16:9 image is approximately 87.2 inches, or 7.26 feet, wide.
7.26 ft × 1.13 = approximately 8.2 ft
The lens should therefore be approximately 8.2 feet from the screen. BenQ uses this type of 100-inch, 1.13:1 example in its projector installation guidance. It is an illustration, not a universal distance for every projector.
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Example: 120-inch 16:9 screen with a 1.15–1.50:1 zoom lens
A 120-inch 16:9 image is approximately 104.6 inches wide.
- Minimum distance:
104.6 × 1.15 = 120.3 inches, or approximately 10.0 feet. - Maximum distance:
104.6 × 1.50 = 156.9 inches, or approximately 13.1 feet.
The usable lens-to-screen interval is therefore about 10.0–13.1 feet, assuming the manufacturer’s published range applies to that image format and the full optical range is available.
How large an image can you create from a fixed distance?
To calculate image width from room distance:
Image width = throw distance ÷ throw ratio
Then calculate diagonal:
Diagonal = image width × √(aspect-ratio width2 + aspect-ratio height2) ÷ aspect-ratio width
Example: 10-foot lens-to-screen distance
At 10 feet, or 120 inches, with a 1.15–1.50:1 projector:
- At 1.15:1: image width is about 104.3 inches, producing a 16:9 diagonal of approximately 119.6 inches.
- At 1.50:1: image width is 80 inches, producing a 16:9 diagonal of approximately 91.7 inches.
The same projector could therefore produce roughly a 92–120-inch 16:9 image from that lens position, subject to the model’s image-format, focus, zoom, and installation limits.
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These are geometric estimates, measured from the lens, and assume a fixed 1.0:1 or 1.5:1 ratio.
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| Screen diagonal | Image width | Distance at 1.0:1 | Distance at 1.5:1 |
|---|---|---|---|
| 80 in | 69.7 in | 5.81 ft | 8.72 ft |
| 100 in | 87.2 in | 7.26 ft | 10.89 ft |
| 120 in | 104.6 in | 8.72 ft | 13.07 ft |
| 150 in | 130.7 in | 10.89 ft | 16.34 ft |
What throw ratio means
Throw ratio describes the relationship between the distance from the projector lens to the screen and the width of the projected image. A lower ratio places a given image size closer to the screen. A higher ratio requires more distance.
“Standard throw,” “short throw,” and “ultra-short throw” are practical descriptions rather than perfectly universal technical categories. Epson broadly describes short throw as around 3–8 feet and ultra-short throw as around 0–4 feet, but manufacturers do not apply these labels identically. The formula remains the same; only the ratio changes.
A short-throw projector can suit a shallow room and reduce the chance of people crossing the beam. An ultra-short-throw projector sits very close to the wall or screen, but its alignment is especially sensitive. Epson’s positioning guide provides brand-specific guidance.
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Optical zoom, digital zoom, and keystone
A throw-ratio range usually indicates an optical zoom lens. For example, the BenQ HT2060 lists a 1.15–1.50:1 throw-ratio range and a 1.3× zoom ratio in its specifications. Optical zoom provides mounting flexibility, although image performance can vary across the lens range.
Do not treat digital zoom or image scaling as an equivalent optical placement range. Digital adjustments crop or resize the image rather than changing the lens geometry. Keystone correction reshapes the image and may reduce effective resolution or geometric fidelity; it should not be used as the primary solution to an incorrectly placed projector.
Measure the installation correctly
The calculated distance normally runs from the lens to the screen surface, not from the wall to the projector’s rear panel. However, manufacturer diagrams may instead identify a projector-front, projector-center, or chassis reference point. Sony’s formula is screen width × lens throw ratio = throw distance, while Epson also directs users to model-specific positioning information.
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Keep these dimensions separate:
- Lens-to-screen distance: the mathematical throw distance.
- Projector-body-to-screen distance: affected by chassis depth and lens location.
- Screen surface position: affected by the wall, frame, border, masking, or recess.
- Mounting position: affected by the bracket, ceiling structure, offset, ventilation, and cables.
A screen advertised as 100 inches may refer to the active image, fabric, or overall frame. Confirm which measurement the manufacturer uses.
Lens shift, offset, and vertical placement
Correct horizontal distance does not guarantee a workable installation. Ceiling height, screen top edge, projector orientation, vertical offset, and lens-shift limits determine whether the image can land on the screen without excessive correction.
Optical lens shift moves the lens-to-image relationship mechanically and is generally preferable to using keystone for permanent placement. A projector with interchangeable lenses must be calculated using the exact lens model, not just the projector body or product family.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Special cases
Golf simulators
Golf-simulator screens often use a 4:3 active image inside a projector with a 16:9 or 16:10 native panel. Use the active projected width, not automatically the full native panel width. BenQ notes this limitation in its golf-simulator guidance. Also allow for ball-impact safety, shadow clearance, projector height, and mounting protection.
Rear projection
The formula still describes lens-to-screen geometry, but rear projection requires additional depth behind the screen, suitable screen material, projector orientation, and possible image flipping.
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Specify whether the calculator expects visible surface width, chord width, or another measurement. “Screen width” is not unambiguous on a curved screen.
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Non-native aspect ratios
A projector’s published throw ratio may assume the full native image width. When using a different aspect ratio, a partial-panel mode, or digital resizing, the active width can differ. Check the model’s manual or installation table.
Manufacturer calculators and manuals
Generic formulas are useful for planning, but the exact projector and lens documentation should control the final installation.
- BenQ Projection Calculator includes model, lens, room, screen, distance, screen position, lens-shift, and installation inputs.
- Epson throw-distance and positioning guide directs users to Epson’s model-specific calculation resources.
- Optoma Projection Calculator provides model-based screen-size and placement planning. Optoma’s support guidance explains key setup specifications.
Calculator databases may be region-specific or incomplete. If a calculator conflicts with the current manual, check whether the two sources use different reference points, lenses, aspect ratios, or tolerances.
Before-you-drill installation checklist
- Measure the available lens-to-screen distance.
- Confirm the screen’s active width, diagonal, aspect ratio, border, and frame dimensions.
- Verify the exact projector and lens model.
- Calculate both endpoints of any optical zoom range.
- Check focus range, lens shift, offset, mount orientation, and ceiling height.
- Add chassis depth, bracket dimensions, screen-wall depth, cable routing, and ventilation clearance.
- Confirm the image fits the usable screen area without relying on excessive keystone.
- Perform a temporary projection test before drilling or permanently mounting.
Troubleshooting
The image is too large or too small
Recheck whether you entered diagonal instead of width, selected the correct aspect ratio, and used the correct end of the zoom range. Then verify the manufacturer’s reference point.
The projector is the right distance but cannot focus
Check the model’s minimum and maximum focus distance, not only its throw ratio. Confirm that the calculated distance is from the lens and that the lens is the correct interchangeable model.
The image is vertically misaligned
Check offset, lens-shift range, screen height, ceiling mount position, and projector orientation. Keystone may make the image appear to fit while reducing usable image quality.
The corners do not fit
Confirm the active aspect ratio, screen surface dimensions, zoom position, digital scaling, and whether the screen is flat. For a curved screen, confirm the width convention used by the calculation.
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UST placement is highly sensitive to height, distance, surface flatness, and alignment. Use the exact model’s installation table and place the projector on a rigid, level surface before making fine adjustments.
Quick Recap
How throw ratio should affect projector selection
- Shallow room: look for a lower throw ratio, short-throw, or UST design.
- Deep room: a standard-throw or long-throw projector may fit better.
- Uncertain mounting location: prioritize optical zoom and useful lens shift.
- Permanent installation: require clear installation drawings and verified offset data.
- Multiple rooms: favor placement flexibility rather than choosing by diagonal alone.
- Bright room: evaluate brightness, ambient light, screen material, and screen gain separately; throw ratio does not determine picture quality.
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