Projector Throw Distance Calculator
Projector throw and screen size from diagonal and ratio.
What it does
Projector placement is a ratio problem before it is a furniture problem. The lens fixes how much width appears per foot of distance, so the screen size picks the seat for the projector. Measuring after mounting means drilling twice.
The tool above turns diagonal and ratio into width and throw. A 100 in screen spans 87.2 in wide, and at ratio 1.5 the lens sits 130.7 in back, about 10.9 ft. The metric match is 254 cm toward 221.4 cm wide with 332.1 cm of throw.
Ratios fall in three lanes: standard near 1.5 and up, short throw from 0.4 to 1.0, and ultra short below 0.4. Zoom lenses quote a range instead of one number, which gives a placement window rather than a point.
Height matters for the mount. A 100 in 16 to 9 image stands about 49 in tall, so the lens offset and screen center set the bracket drop. Confirm offset in the manual after the distance math.
How to use
- Pick imperial (in, ft) or metric (cm, m).
- Enter screen diagonal: 100 in or 254 cm.
- Enter throw ratio from the lens spec.
- Read screen width first.
- Read throw distance with feet or meters.
- Read screen height for mounting.
Formula
- diagonal
- Screen diagonal in matching units.
- ratio
- Lens ratio: distance over width from the spec sheet.
- 0.8716
- 16 to 9 width factor, 16 / root(337).
Throw ratio equals throw distance divided by image width, with standard, short throw, and ultra short classes from AV installation guidance. The 16 to 9 factors come from 16 over root 337 for width and 9 over root 337 for height. Zoom lenses give a ratio range, so run the tool twice for placement limits.
Worked example
Example: 100 in at 1.5 ratio
Imperial defaults: 100 in diagonal at 1.5 ratio. These are also the default values, so the page opens on this answer.
- Screen: 100 in diagonal, 16 to 9.
- Width: 100 x 0.8716 = 87.16, shown as 87.2 in.
- Height: 100 x 0.4903 = 49.03, shown as 49 in.
- Ratio: 1.5.
- Throw: 87.16 x 1.5 = 130.74, shown as 130.7 in.
- Feet: 130.74 / 12 = 10.90, shown as 10.9 ft.
- Tool shows 87.2 in wide with 130.7 in (10.9 ft) of throw.
- Metric match: 254 cm gives 221.4 cm wide with 332.1 cm (3.32 m) of throw.
Reference table
| Diagonal | Width | Throw |
|---|---|---|
| 80 in | 69.7 in | 104.6 in (8.7 ft) |
| 100 in | 87.2 in | 130.7 in (10.9 ft) |
| 120 in | 104.6 in | 156.9 in (13.1 ft) |
| 100 in at 0.8 | 87.2 in | 69.7 in (5.8 ft) |
Limits
- Fixed ratio math; ignores lens shift and offset.
- Assumes 16 to 9 screens.
- Zoom needs two runs for min and max.
- Room light and gain ignored.
Common mistakes
- Reading diagonal as width.
- Mounting before computing throw.
- Using one ratio for a zoom lens.
- Forgetting offset drops the image.
- Ignoring screen height for the mount.
Try it yourself
Quick checks. Answers sit tucked under each question.
90 in at 1.5?
Width 78.4 in with throw 117.7 in (9.8 ft).
254 cm at short throw 0.8?
Width 221.4 cm with throw 177.1 cm (1.77 m).
Questions
How is throw found?
Multiply screen width by the throw ratio. Here 87.2 x 1.5 = 130.7 in.
How is width found?
Multiply diagonal by 0.8716 for 16 to 9. Here 100 x 0.8716 = 87.2 in.
Throw ratio classes?
Standard near 1.5 and up, short throw 0.4 to 1.0, ultra short below 0.4.
Zoom lens?
Zoom lenses list a range, so compute both ends for min and max placement.
Exact for every projector?
No. Offsets, lens shift, and screen gain shift the image without moving the math much.
Metric version?
Same steps in cm: 254 cm gives 221.4 cm wide with 332.1 cm of throw.